World Hopping (HLC)

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World Hopping  A visit to a foreign land, long or short, is seldom routine. Dealing with strange customs, unfamiliar laws, and unusual foods can give even hardened travelers fits. Now imagine what it might be like to visit a place where the very underpinnings of reality are different from home. That's what world hopping is like.
Staging adventures on unfamiliar worlds is a great way to keep a high-level campaign fresh and challenging. Players become very attentive once they find they can take nothing for granted, and even fairly weak creatures can challenge the party when the PCs' spells and magical items begin to act in unanticipated ways. This section presents some quick guidelines for creating alternate worlds for your adventures. This section is by no means complete—the possibilities are limited only by your imagination.
==Types of Worlds==
For purposes of this discussion, a world is any place in the multiverse with its own form of reality separate from the rest of the multiverse. A world can be as large as a universe or as small as a single room. Worlds in the current AD&D game fall into one of three different types:
==Plane==
A plane is an infinitely large space. A plane has no clear form or dimensions, though there are border areas where it meets other planes. As explained in Chapter 15 of the Dungeon Master Guide, there are three types of planes and two planes that defy categorization.
Inner Planes are places filled with the fundamental components of the multiverse. There are 18 inner planes. They are subdivided into elemental (basic matter), para-elemental (compound forms of matter), energy (positive and negative), and quasi-elemental (where planes of matter and energy meet). If there are any undiscovered inner planes, they likely exist between known planes.
Outer Planes are places where the powers (deities) reside. A certain philosophy holds sway on each outer plane, and that philosophy influences everything on the plane, including reality itself. There are 17 known outer planes, each corresponding to a major division in the AD&D alignment system. Sixteen of these planes form a great ring, with the plane of Concordant Opposition—the neutrality plane known as the Outlands—in the middle. New outer planes would probably form between two existing planes on the great ring or as additional “layers” on an existing plane.
The Prime Material Plane is where the base campaign and many similar worlds are located. There is a widespread misconception that there are multiple Prime Material Planes, sometimes referred to as Parallel Primes or Alternate Primes. In fact, there is only one Prime Material Plane. Within that plane, there are an infinite number of discrete worlds, each contained within a crystal sphere. A crystal sphere can contain a single planetary body, a whole solar system, or anything in between.
The Astral and Ethereal Planes act as highways between the other planes.
The Ethereal Plane connects the Prime Material with the Inner Planes. It resembles an infinite ocean whose “shores” lap against other planes. Curiously enough, ethereal travelers always find themselves moving toward the Inner Planes or their home world in the Prime Material. There is no known method of using the Ethereal Plane to travel from one Prime Material World to another.
The Astral Plane is an infinite, silvery void that connects the Prime Material Plane to the Outer Planes. Astral travel between Prime Material Worlds is possible.
Both the Astral and the Ethereal contain bits of solid matter in their depths. On the Astral, these form islands similar to asteroids floating in deep space where creatures make their homes. The Ethereal also contains islands, but they are called Demiplanes (see below) that exist as worlds in their own right.
For more information on the known planes, see the Planescape™ boxed set.
==A Pocket Dimension==
is a discrete world attached to another world. These are usually very small, and most of their properties mirror those of the parent world. A Pocket Dimension can be created artificially.
==A Demiplane==
is a discrete world floating in the depths of the Ethereal Plane. Like Pocket Dimensions, Demiplanes can be created artificially. Conditions on Demiplanes vary widely, and it is believed that large and well-populated Demiplanes can become full-fledged planes. The exact process for accomplishing this feat is not known to any mortal.
==Properties of Worlds==
Each world has four different aspects that combine to define its own unique reality. These are chronology, magic, technology, and environment. Each aspect is rated on a scale ranging from 2 to 20. Ratings can be generated randomly by rolling 2d10. The lower the rating, the weaker the aspect is; ratings from 10–12 reflect conditions on typical AD&D campaign worlds. Though a rating of 10 is weaker than a rating of 12 the differences between the two are imperceptible to player characters. Ratings higher than 20 and lower than 2 are possible, but all known planes fall within these extremes.
A world's rating is usually fixed, but the ratings on some worlds shift slowly over time. These shifts are so gradual that the residents don't realize they are occurring. An abrupt shift—even for the better—brings cataclysmic change to a world.
==Chronological Aspect==
Time flows at the same rate throughout the known multiverse. This section, however, deals with newly discovered worlds. Table 2 shows the rate of local time flow compared to that of the base campaign world. In worlds with ratings of 9 or less time flows more quickly than in the base campaign, allowing travelers to make extended visits and return home to find that almost no time has passed at all. In worlds with ratings of 13 or more time flows more slowly than in the base campaign, and travelers might return home to find their world greatly changed after even a short visit.
==Chronological Notes==
Characters are governed by the local time no matter where they are or what world they call home. For example, characters who visit a C2 world and stay a year return home to find that less than a minute has gone by, but they are still a year older. Characters who visit a C18 world and stay two weeks return to find that 20 years have passed, even though they have aged only two weeks. Likewise, the durations of magical effects are governed by local time, a spell that lasts 10 rounds on a C11 world also lasts 10 rounds on a C20 or a C2 world.
There is no simple way to judge the local time flow—it always seems to be normal. Time is pervasive; even the interiors of closed extra-dimensional spaces (such as portable holes, bags of holding, and rope trick spells) experience local time. The shift from one time flow to another is imperceptible by itself, but clues are sometimes obvious—such as when a character steps through a portal at noon and steps out into a moonlit night.
==Magical Aspect==
A world's magical rating determines many of its characteristics, including how much sway scientific laws have over reality. The higher the rating, the less relevant the laws of science are. Magic becomes more readily available as the magical rating rises, increasing the likelihood that fantastic creatures exist on the world. Psionics are also more common and work better on high-magic worlds. Table 3 shows relative levels of magical power; a rating of 2 indicates no magical power, a rating of 10–12 indicates the level of power in a typical AD&D campaign. The most magical of the known planes (the Abyss, the Outlands) have ratings of 17. No known plane has a rating of 18 or higher.
 Table 2: Chronological Ratings
WorldRating	LocalTime	Base CampaignTime
2 	1 Week 	= 1 Second
3 	1 Week 	= 15 Seconds
4 	1 Week 	= 1 Minute
5 	1 Week 	= 10 Minutes
6 	1 Week 	= 30 Minutes
7 	1 Week 	= 1 Hour
8 	1 Week 	= 6 Hours
9 	1 Week 	= 1 Day
10–12 	1 Week 	= 1 Week
13 	1 Week 	= 1 Month
14 	1 Week 	= 3 Months
15 	1 Week 	= 6 Months
16 	1 Week 	= 1 Year
17 	1 Week 	= 5 Years
18 	1 Week 	= 10 Years
19 	1 Week 	= 30 Years
20 	1 Week 	= 100 Years
 Table 3: Magical Ratings
Rating	Magical Effects
2 	No spell, spell-like ability, magical item, artifact, or psionic power functions, and travel into or out of the area is possible only through a pre-existing gate. Land creatures are not more than 10 feet tall, and there are no flying creatures. Demihuman and fantastic creatures do not exist.
3 	Potions, wands, rings, and miscellaneous magic is ineffective, and from 6–9 schools of magic are modified in some way. Spell casting times and PSP requirements are quintupled, and 4th–10th level spells can’t be cast. Land creatures are not more than 10 feet tall, and flight is limited to creatures less than six inches tall. There are no demihumans or fantastic creatures.
4 	Potions, wands, and rings are ineffective and from 4–9 schools of magic are modified in some fashion. Spell casting times and PSP requirements quintupled; 5th–10th level spells impossible; land creatures are not more than 10 feet tall; flight is limited to creatures less than 1-foot-tall. There are no demihumans or fantastic creatures.
5 	Potions and wands ineffective; 3–9 schools of magic modified. Spell casting times and PSP requirements are quintupled, and 6th–10th level spells can’t be cast—native spellcasters are almost unknown. Land creatures are not more than 10 feet tall, and flight is limited to size T creatures (two feet tall or less). There are no demihumans or fantastic creatures.
6 	Potions are ineffective and from 3–9 schools of magic are modified. Spell casting times and PSP requirements quadrupled, and 7th–10th level spells can’t be cast. Native spellcasters are very rare and have supra-genius Intelligence. There are no land creatures more than 15 feet tall, no bipedal creatures more than 10 feet tall, and flight is limited to size S or smaller creatures.
7 	Most spells, magical items, and psionics function normally, but 2–7 schools of magic are modified. Spell casting times and PSP requirements are tripled, and 8th–10th level spells cannot be cast. With long and difficult training, a few creatures of at least genius Intelligence can learn to cast spells. There are no land creatures more than 20 feet tall, no bipedal creatures more than 15 feet tall, and flight is limited to size M or smaller creatures.
8 	Most spells, magical items, and psionics function normally, but 2–5 schools of magic are modified. Spell casting times and PSP requirements are doubled, and 9th–10th level spells can’t be cast. With training, a few creatures of at least exceptional Intelligence can learn to cast spells. There are no land creatures more than 25 feet tall, no bipedal creatures more than 20 feet tall, and flight is limited to size L or smaller creatures.
9 	Most spells, magical items, and psionics function normally, and only1–4 schools of magic are modified. True Dweomers (10th-level spells) are not available, but creatures with at least average intelligence can learn to cast spells if properly trained. There are no land creatures more than 30 feet tall, no bipedal creatures more than 25 feet tall, and flight is limited to size H or smaller creatures.
10-12 	Spells, magical items, and psionics function normally, and most creatures of at least average Intelligence can learn to cast spells with adequate training. There are no practical limits on the size of land or of flying creatures, and demihumans and fantastic creatures are fairly common.
13 	Spells, magical items, and psionics function normally, and major races have minor spell-like abilities or psionic wild talents. Some individual spells are modified.
14 	Most spells, magical items, and psionics function normally, and major races have minor and major spell-like abilities or multiple psionic powers. Some elemental spells and from 1–4 schools of magic are modified.
15 	Most spells, magical items, and psionics function normally, and major races have minor, major, and extraordinary spell-like abilities or full psionic powers. Some elemental spells are modified. From 2–5 schools of magic are also modified with possibly catastrophic effects.
16 	Same as above, except that from 2–7 schools of magic are modified with possibly catastrophic effects.
17 	Same as above, except that from 3–9 schools of magic are modified with possibly catastrophic effects.
18 	Same as above, except that most beings of at least average Intelligence have minor spellcasting abilities.
19 	Same as above, except that beings of average Intelligence have minor spellcasting abilities, and those with at least high intelligence have major spellcasting abilities. Wizard characters do not need to study spellbooks.
20 	Same as above, except that beings of average intelligence have major spellcasting abilities, and those with at least high Intelligence have extraordinary spellcasting abilities. Wizard characters do not need to study spellbooks, and no spellcaster needs to memorize spells.
==Magical Aspect Notes==
Characters using magic or psionics are often at great risk until they learn the rules governing magic locally. Strongly magical worlds can be more dangerous than worlds where magic is weak.
==Spell Casting==
Any spellcaster can attempt spells on worlds rated M3 or higher, but he is limited to what is possible locally or what is possible on their home worlds, whichever is less. For example, characters from M10–12 worlds must study their spellbooks even on M20 worlds, where the natives have no such restrictions. Characters from an M19 world visiting a M10–12 world cannot regain spells unless they return to their home world or acquire spellbooks. No character can cast a 9th-level spell on a world rated M8 or lower.
Low magic worlds impose a multiplier (x2 to x5) on casting times. Most casting times are given as simple numbers that are added to the caster's initiative roll (see Player's Handbook, Appendix 2). If the adjusted casting time is 10 or more, the spell requires one or more full rounds to cast. A casting time of 10 means the spell is completed at the end of the round when it is begun. A casting time of 20 means the spell is completed at the end of the second round after it has begun, and so on. If the adjusted casting time is not an even multiple of 10, subtract the nearest multiple of 10 from the adjusted casting time. The spell requires that many full rounds of casting, and is completed on the next succeeding round with an initiative modifier equal to the remainder. For example, a fireball spell (which has a normal casting time of 3) has an adjusted casting time of 12 on an M6 world. The spell requires one full round and is completed during the second round with an initiative modifier of 2.
Worlds rated M8 and lower restrict the levels of spells available. When a spell level becomes impossible, no spell of that level can be cast. Magical items and stored spells are an exception (see below).
Spells are modified on some worlds. Modifications can apply to individual spells, entire schools of spells, or classes of elemental spells. Possible modifications include:
Enhanced: The spell or school functions as though the caster were one level higher than he actually is. Spells are never enhanced on worlds rated M9 or lower.
Diminished: The spell or school functions as though the caster were one level lower than he actually is.
Nullified: The spell or school does not function at all. This is a fairly common modification on worlds rated M9 or lower. It is rare on Prime Material Worlds rated M10 or higher, but it often occurs on even highly magical outer planes, demiplanes, and pocket dimensions.
Altered: The spell or school of spells functions differently on this world. Changes can be superficial, minor, or catastrophic.
Superficial alterations usually change a spell's form, but not the way it works. For example, fireballs might create scalding steam or intense light on some planes.
Minor alterations are more spectacular and potentially dangerous but do not change the way the spell works. For example, a clairaudience spell might cause the caster's ears to grow very large and sensitive, causing the caster to suffer a saving throw penalty vs. sound-based attacks (harpy songs, shout spells, etc.) until the spell ends.
Catastrophic alterations cause the spell to go completely awry, and their effects are totally unpredictable. Conjured or summoned creatures might go berserk, a meteor swarm might center itself on the caster, or a death spell might target other player characters or their henchmen.
In many cases, native spellcasters are not subject to the alterations because their magic is naturally compatible or because they take special precautions. Player characters might learn to use the latter.
It is possible for the same alteration to affect several types of spells in the same way. For example, on Limbo, an outer plane of pure chaos, a spellcaster must pass an Intelligence check or any spell attempted is negated, a catastrophic alteration that affects all types of spells.
Any change to a spell or school of spells should reflect some local characteristic. For example, an unseen servant spell cast on an M13 world that also has a high technological rating might suffer a minor alteration and create a visible creature with a mass of robot-like arms (in keeping with the world's technological nature).
Priests depend on their deities for their spells and suffer some extra difficulties when leaving their home worlds. Any priest spell is subject to whatever local modifications apply to the spell's school. In addition, a priest's ability to cast spells depends on his position in the multiverse relative to his deity.
Priest spells work best when the caster is on the plane where his deity resides because the deity has undisputed influence over priest magic on his own plane. Deities that keep multiple residences make things a lot easier for their priests. When priests go traveling through the multiverse, however, they enter realms where the interests of several deities might conflict. One of four things happen to a priest's spells when the character enters a new world:
On an open world, the priest loses caster levels according to the distance to the deity's home plane (see page 49). All the Outer Planes are open.
On a closed world, the priest can use any spell he has memorized but cannot regain spells higher than 2nd level. Many Prime Material Worlds, Pocket Dimensions, and Demiplanes are closed.
On a restricted world, the priest loses all spells. Restricted worlds are very rare.
On an unrestricted world, all priests function at full power. The Astral, Ethereal, and all known Inner planes are unrestricted, as are many Prime Material worlds and Demiplanes.
By general divine agreement, priests on open worlds lose one level of spell casting ability for every plane they are removed from their deity's home plane. For example, a 10th-level priest one plane from his deity's plane can cast spells only as a 9th-level priest, although he still functions as a 10th-level character in every other way.
Figuring the distance between a priest and his deity can be a little tricky, because priest spells use different rules for counting depending on the priest's location. A priest whose deity resides on an Inner Plane is four planes removed when he visits an Outer Plane (Inner Plane to Ethereal to Prime to Astral to Outer Plane). Priests on the Outer
Planes, however, must trace the path to their deity along the great ring (see below), but only planes between the priest and deity's home plane count.
For example, if a priest whose deity resides on Mount Celestia visits The Abyss, the character loses seven levels of spellcasting ability. This effect has nothing to do with the properties of the planes themselves, it arises from a mutual agreement that prevents the entire multiverse from erupting into an interplanar war.
There are numerous divine agreements of a more limited nature that govern specific locations on the planes. The Prime Material Plane is subject to many such agreements. Each Prime Material world is the focus of one or more deities; these deities are allowed to treat the world as if it were home (at least insofar as granting spells is concerned). This gives any priest who worships these deities full powers on that world, though outsiders might find the world closed or restricted.
Demiplanes also are notorious for operating under their own rules, though most of them are either closed or unrestricted.
A priest's granted abilities generally function at full power by general divine agreement, but local conditions prevail, especially for spell-like granted abilities. Calling down a flame strike just doesn't work on the Plane of Elemental Water.
Note that divine agreement can circumvent a world's magical rating. If a deity wants to grant priests a full range of spells, then that's what happens, even if magical items, psionics, and wizards spells are weak. Such worlds are extremely rare, but possible.
Intelligent creatures native to high-magic worlds have natural spellcasting abilities as spellcasters of the indicated level:
Minor Spellcasting: 1st–3rd
Major Spellcasting: 4th–7th
Extraordinary Spellcasting: 8th–11th
Natural spellcasting abilities are retained if the creature visits worlds with lower magical ratings, but casting times are still extended and high-level spells still become unavailable as shown on Table 3. Natural spellcasting abilities are in addition to any abilities the creature has due to class and level and can be freely combined with other class abilities. For example, a fighter from an M20 world could cast natural spells even in metal armor; a wizard from the same world is still restricted from wearing armor but might enjoy extra wizard spells or have the ability to cast priest spells.
On worlds rated M19 or higher, wizards don't require spellbooks. After a good night's sleep, spellcasters can meditate and acquire any spell of a level normally available to them, just as priests do.
On worlds rated M20, wizards and priests do not require study time at all. If they get a good night's sleep, they can call their spells to mind as needed, though they are still limited to the number of spells they can employ each day. Casting time and required components for spells remain unchanged. For example, an 11th-level wizard from an M20 world could call a lightning bolt to mind if he wished, but not if he had already cast four 3rd-level spells that day. The wizard would also need to have the proper material components on hand.
==Psionics==
Psionicists generally suffer less than spellcasters when traveling between worlds. Psionics depend on the character's personal energies, which the character carries with him wherever he goes. On high-magic worlds (M13 or greater), psionics are unaffected, though some worlds—such as the Demiplane of Ravenloft—have quirks that affect even psionics. On low-magic worlds (M9 or less), psionics work normally, but PSP costs increase because more personal energy is required to manifest a particular effect.   Increased PSP requirements apply to both initiating and maintaining powers. If a psionicist does not have enough PSPs to pay the local cost for a power, he cannot use that power. Local conditions only increase the PSP cost, never the damage dice, duration, range or any other factor associated with a PSP expenditure. In other words, increased psionic cost is never an advantage for the character using the power.
A major race dominates the world in the same fashion that humans and demihumans dominate standard campaign worlds. The tanar'ri of the Abyss and the githyanki of the Astral Plane are major races in their home worlds. Members of major races native to high-magic worlds always have one or more spell-like abilities, as follows:
Minor abilities: Similar to 1st–2nd level spells, each of these abilities is usable 1–3 times a day. They function on worlds rated M7 or higher.
Major abilities: Similar to 3rd–5th level spells, each ability is usable 1–3 times a day. The creature also has 4–6 minor abilities each usable once a turn or once an hour. The abilities function on worlds rated M8 or higher.
Extraordinary abilities: Similar to 6–7th level spells, each is usable once a day. The creature also has 6–10 minor abilities usable at will and 4–6 major abilities usable once a turn or once an hour. The abilities function on worlds rated M9 or higher.
Spell-like abilities are subject to whatever magical modifications prevail locally, except that natives always ignore any detrimental effects their home world might have on their abilities.
==Magical Items==
Because they are portable containers for magical power, enchanted items can often function in low-magic worlds where the spell effects they duplicate cannot be cast. Otherwise, magical items are subject to the same limitations and modifications as spells. For example, a staff of the magi can produce a wall of fire effect, even on M3 worlds where 4th-level spells are impossible. However, the staff cannot produce a wall of fire on a world where evocation spells are nullified or on a world where fire spells don't work.
If a school of spells is modified on a world, all magical items that duplicate or simulate effects from that school are affected as well. For example, if conjuration/summoning spells are catastrophically altered on a world, items such as Bucknard's everfull purse and a bag of tricks can be dangerous to use.
Magical weapons, armor, and protective devices, such as rings of protection and bracers of defense, are attuned to the world where they were made. They lose one plus per plane removed from home, but remember that all Prime Material worlds are on the same plane. The Astral and Ethereal planes are one plane removed from the Prime Material. The Inner and Outer Planes are two planes removed from the Prime Material. Demiplanes are part of the Ethereal Plane and Pocket Dimensions are part of the plane to which they are attached. The maximum distance between planes is four (Inner Plane to Ethereal to Prime
Material to Astral to Outer Plane). For example, a cloak of protection +3 made on a
Prime Material world functions normally everywhere on the Prime Material Plane. The cloak's bonus falls to +2 in the Astral or Ethereal planes, and falls to +1 on any Outer or Inner plane. Unlike priest spells, magical items always trace the shortest possible path to their home planes.
Magical items that become inert because of the local magical rating or because of the distance between planes cannot produce any magical effects but still function as normal items—an inert suit of magical armor is still armor. The items continue to have a magical aura that can be discerned with a detect magic or similar spell, and they function normally again once brought to a world where conditions are more favorable.
==Creatures==
A world's magical factor determines what kinds of fantastic creatures can be found within it, as noted on Table 3. The local magical factor can make a world untenable for some visitors.
Humans, normal animals, and other non-fantastic creatures are not directly affected by the local magical rating.
Other creatures are dependent on their home world's magical nature and can suffer from deprivation when visiting low-magic worlds.
Demihumans, such as elves, gnomes, dwarves, orcs, ogres, and similar humanoid creatures, must save vs. death magic immediately when entering worlds rated M5 or less, failure results in death. Even if the saving throw succeeds, the creature loses one hit point per hit die—but each hit die still gives the creature a minimum of one point—and suffers a –1 penalty on all attacks, saving throws, and ability score checks. These penalties increase an additional point for every magical rating below 5, to a maximum penalty of –4 on an M2 world.
Fantastic creatures, such as centaurs, dragons, chimeras, pixies, tanar'ri and others, have similar penalties beginning at M6 and increasing to a maximum of –5 on M2 worlds.
==Technological Aspect==
A world's technological rating determines its general level of cultural development, scholarship, and practical application of knowledge and invention. The lower a world's technological rating, the less obvious the trappings of civilization are. A rating of 2 indicates no technology at all. A rating of 10–12 indicates a medieval technology common to most AD&D campaigns. Ratings of 13 or higher indicate worlds that are progressively more urban, institutional, and mechanized. It is entirely possible for a world to have both a high magical rating and a high technological rating. On such worlds, magical devices replace machines.
 Table 4: Technological Ratings
Rating	Elements of Civilization
2 	Tools are unknown; fire has not been harnessed.
3 	Simple stone tools and weapons; campfires.
4 	Complex stone tools, some soft metal tools and weapons (copper); domesticated animals; simple agriculture; ovens; pottery.
5 	Soft metal tools and weapons (copper and bronze); arithmetic; complex agriculture and irrigation; hieroglyphic writing; boats; cities; sundials and water clocks; coins.
6 	Hard metal tools and weapons (iron); small ships; alphabetic writing; small land vehicles; simple locks; siege machines.
7 	Water mills; furnaces; cast iron; large oared ships; advanced mathematics and philosophy.
8 	Civil engineering; roads; blown glass; wagons; medicine.
9 	Compass; windmills; universities; surgery.
10–12 	Steel tools and weapons; coal mining; trade and craft guilds; small, slow sailing ships, feudal governments; extensive trade.
13 	Cannons; ocean-going sailing ships; mechanical clocks; national
governments.
14 	Firearms; printing; intercontinental trade.
15 	Steam engines; blast furnaces; mechanical calculating machines.
16 	Internal combustion engines; light aircraft; steamships; railroads; labor unions.
17 	Nuclear power; civil and military aircraft; electronic computers.
18 	Fusion power; commercial spacecraft; laser weapons; genetic engineering; intercontinental governments.
19 	Sentient robots and computers; solar power; portable nuclear power.
20 	Faster-than-light space travel; matter transmission; matter replication; interplanetary governments.
==Technological Notes==
Sample items appear on the table when they become affordable or are in common use. Some items may be present, but very rare, on worlds with technological ratings too low to support their widespread use. For example, some brilliant thinker might be busy inventing algebra on a T5 world, but she might be the only one who understands it. Likewise, items on the table are not necessarily household items. For example, not everyone on a T17 world owns a jet airliner, but they are common enough to be in general use.
Technological devices cannot be carried freely between worlds. Devices from low-technology worlds function normally when carried to worlds with higher technology ratings. Devices carried from high-technology worlds to low-technology worlds do not operate if they have moving parts, electronic circuitry, or depend on chemical reactions. Even simple devices suffer somewhat. For example, a flashlight (T16) carried to a T8 world becomes inert. A stainless steel hand ax (also T16) carried to a T8 world still functions as an ax, but it loses its extra hardness and resistance to rust. A club (T2) remains a club no matter where it is.
Sufficiently advanced technology, however, works just like magic. If an item's technological rating exceeds the local technology rating it still works if it also exceeds the local magical rating by at least five. For example, steam engines require a local technology rating of T15 or higher or a magical rating of M10 or lower. A steam engine would not work on a world with a magical rating of M11 or more and a technological rating of T14 or less.
==Ecological Aspect==
A world's ecological rating determines how benign or hostile the overall environment is as well as the similarities of landscape, flora, and fauna as compared to the base campaign. A rating of 2 indicates a completely hostile environment while an E20 world represents a paradise. A rating of 10–12 indicates a generally earth-like environment that may contain hazardous extremes, such as deserts, ocean depths, low air pressure at high altitude, etc.
==Ecological Notes==
Worlds rated E6 or less inflict one of more of the effects (DM's choice) from the table below upon visitors from the base campaign. The type of effect should reflect the nature of the environment. For example, one world's acidic atmosphere might inflict damage and another world's polluted air might reduce Constitution.
Condition 	Severe 	Hostile 	Deadly
Constitution	 	 	
Loss 	1d6/Day	1d6/Hour	1d6/Round
Damage 	2d4/Day	2d4/Hour	2d4/Round
Poison Save*	1/Day 	1/Hour 	1/Round
: * The saving throw must be attempted at the end of each exposure period; failure results in immediate death.
Severe Conditions: The environment poses a danger if exposure lasts too long. The intensity is similar to a desert or polar ice cap. Mundane precautions—drinking extra water, wearing a heavy coat—can negate or reduce the damage.
Hostile Conditions: The environment poses an immediate threat to normal humans. The intensity is similar to immersion in arctic water or exposure to volcanic gases. Mundane precautions might reduce the effects to severe or be entirely ineffective. Minor protective magic, such as an endure cold/heat spell, ring of fire resistance, or ring of warmth, negates the effects.
Deadly Conditions: The environment can kill normal humans within minutes. Intensity is similar to the surface of the moon or the interior of a volcano. Mundane precautions are ineffective, and some magical items or spells might prove too weak to provide effective protection. The deadly effects listed on the table are the minimums, and they can be much greater if conditions are particularly intense. For example, the flames on the Plane of
Elemental Fire require unprotected creatures to save vs. breath weapon or die immediately. A successful save still inflicts 5d10 points of damage each round.
Worlds rated E18 or higher seem like paradises to visitors from worlds rated E12 or less. At the DM's option, certain actions can be perilous on such worlds. For example, characters who go to sleep on such worlds may slumber until attacked or awakened. Smelling a flower might produce a state of euphoria similar to a confusion spell, although random actions tend to be non-violent; if the dice roll indicates an attack the affected character sings and dances, perhaps urging other nearby creatures to join in.
Natives of worlds rated E16 or higher generally cannot tolerate conditions on less benign worlds. They suffer the effects from severe conditions on worlds rated five less than their home worlds, hostile penalties on worlds rated six less, and deadly penalties on worlds rated seven or more less.
 Table 5: Ecological Ratings
Rating	Ecological Elements
2 	The ecology is wildly different from the base campaign in almost every way; the environment is deadly (poisonous, airless, acidic, etc.). Living creatures, if they exist at all, are barely recognizable as such.
3 	The ecology is different from the base campaign in most ways; the environment is hostile (very cold, waterless, flooded with x-rays, etc.). Living creatures have completely alien forms.
4 	The ecology is similar to the base campaign. The environment is fairly livable, but some vital element is absent or incompatible. The PCs cannot survive over the long term without a large stock of supplies from their home world or magical aid (can’t eat the food, water makes PCs drunk, etc.). Overall conditions may be hostile, such as boiling daytime temperatures, subzero nighttime temperatures, acid rain, etc. One or more intelligent races resemble some nonhumanoid or monstrous species (insects, serpents, fungi, etc.).
5 	The ecology is similar to the base campaign. The environment is livable, but some vital element is absent or incompatible. The PCs cannot survive over the long term without a large stock of supplies from their home world or magical aid (can’t eat the food, water makes PCs drunk, etc.). Overall conditions may be severe, such as a global desert, ice age, endless rain, etc. One or more intelligent races resemble some nonhumanoid or monstrous species (insects, felines, fungi, etc.).
6 	The ecology is similar to the base campaign. The environment is livable, but some important element is absent or incompatible. The PCs may find the conditions inconvenient, but their long-term survival is not in jeopardy (little or no metal, thin atmosphere, sunless sky, etc.). Overall conditions may be severe, such as a global desert, ice age, endless rain, etc. One or more intelligent races resembles some nonhumanoid or monstrous species (insects, felines, dragons, etc.).
7 	Ecology is similar to the base campaign. Some familiar races and species are present, though they have slightly different appearances and abilities. Races and species entirely unknown in the base campaign are present. At least one intelligent race resembles some nonhumanoid species (lizards, felines, avians, etc.).
8 	Ecology is very similar to the base campaign, and the environment is generally benign. Many familiar races and species are present, though they have slightly different appearances and abilities. Races and species entirely unknown in the base campaign are present.
9 	Ecology is very similar to the base campaign. Most familiar races and species are present, though some may have slightly different appearances or abilities.
10–12 	Ecology, environment, and inhabitants are almost identical to the base campaign.
13 	Ecology and environment is almost identical to the base campaign. All major races and species are present, but the world is ruled by elves, gnomes, dragons, or other race that is not dominant in the base campaign.
14 	Ecology and environment is almost identical to the base campaign. All major races and species are present, but not all races have the same level of Intelligence and culture as they do in the base campaign (humans with only animal intelligence, talking horses, ogre artists, etc.).
15 	Ecology and environment are almost identical to the base campaign. All major races and species from the base campaign are present, but some general characteristic is vastly different worldwide (everything is giant-sized, colors are reversed, world is flat, etc.).
16 	Ecology is very similar to the base campaign, and the environment is generally favorable (completely tropical, rains according to a predictable schedule, most plants edible, etc.). Most races and species from the base campaign are present, but local species tend to be exotic, such as flightless giant parrots, feathered snakes with iridescent plumage, or birds who sing highly musical songs.
17 	The ecology is similar to the base campaign, and the environment is favorable(tropical with temperate nights, never rains, all plants edible, etc.). At least one intelligent race resembles some nonhumanoid species, such as elves that look like felines.
18 	The ecology is slightly similar to the base campaign, and the environment is
favorable (drinking the local water provides nourishment, sleeping is not necessary, equipment grows on trees, etc.). One or more intelligent races resemble some nonhumanoid or monstrous species (insects, serpents, fungi, etc.).
19 	The ecology is different from the base campaign in most ways, and the environment is very favorable (constant temperature, breathing supplies nourishment, sunlight heals wounds, etc.). Living creatures have completely alien forms.
20 	The ecology is wildly different from the base campaign in almost every way, and the environment is completely favorable (eating, sleeping, and drinking unnecessary). Living creatures exist, but are barely recognizable (pure energy, rocklike, microscopic).
==Quirks==
In addition to the four aspects—chronological, magical, technological, and environmental—some worlds have additional properties that help make them unique and unpredictable. These properties—quirks—are not easily categorized. Quirks can be part of a world's essential makeup, completely serendipitous, or temporarily imposed from outside. In the latter two cases, the player characters might be able to change them. The local rules governing priest spells described on page 49 can be considered essential quirks. A few known quirks are listed below:
The world is infused with some overwhelming force or energy that twists everything, including magic and psionic abilities. For example, the Demiplane of Ravenloft is infused with evil. No spell, granted ability, or psionic power can distinguish the alignment of any creature or object on Ravenloft, and many magical effects and psionic powers are corrupted.
Other worlds might be infused with good, light, magic, electricity, or anything else that can be detected or manipulated under the AD&D game rules.
If this quirk exists on a Prime Material world, it's probably a temporary effect that can be removed if the source is destroyed. Otherwise, it cannot be altered or removed except by destroying the entire world.
A particular type of material is difficult or impossible to magically conjure or duplicate on the world. For example metal is very rare on Athas, the world of the Dark Sun™ setting. Metal cannot be permanently created on Athas, and the normally permanent wall of iron spell quickly falls to pieces.
Spells that have been named after their creators (such as Melf's minute meteors) are unknown and unavailable unless brought in from outside or researched from scratch.
Leaders of the world's dominant race are able to detect and immediately retaliate against magical or psionic attacks  directed against members of the race. This quirk is possible only on worlds rated M14 or higher. Retaliation can take whatever form the DM feels is appropriate: a simple spell turning effect, one large venomous insect attacks the offender for every point of damage inflicted on the target, a random spell is directed at the offender, etc.
Magical items brought into the world are not affected by the distance to their home planes but are subject to other local effects. Such worlds usually are unrestricted (see page 49) and have a magical rating of 13 or higher.
The world traps visitors. Exit is possible only through pre-existing gates. This quirk is possible only in Demiplanes and Pocket Dimensions.
The world and some or all of its residents are analogs to beings in the base campaign. If the two world's ratings are generally similar, analogous beings from the two worlds are virtual twins, having appearances, occupations, skills, and alignments similar to their twins'. The more the two world's aspects diverge, the more dissimilar the analogs are.
Worlds that contain player character analogs present all sorts of difficulties and opportunities for the PCs:
==Same Book, Different Cover==
Analogs have completely different appearances, but identical mannerisms and similar histories. How long does it take the group to realize that the arrogant lizard man they are dealing with is just another version of a PC wizard?
Don't Judge a Book by its Cover: Analogs look and act pretty much like their counterparts, but they have different dispositions and skills. Perhaps the player character analogs on this world are notorious villains or perhaps the PCs' chief rival is a great and revered hero here.
==Déjá Vu==
The world might contain analogs whose counterparts have died in the base campaign, both foes and allies. Also, the current situation on this world might mirror an adventure the PCs have already completed, but the villains have made different plans this time.
The world parallels the base campaign and is actually a version of the base campaign's past or future.
Some mundane item from the base campaign is the focus for power on this world. For example, powdered dragon horn explodes like gunpowder, gold jewelry grants a spell-like power, etc.
The world is isolated from other dimensions. Extradimensional spaces, such as those created by portable holes, rope trick spells, and bags of holding, cannot be opened.