Mages and Magic (PWH)

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Planewalking wizards have a lot to remember. They've got to keep track of how their spells interact with the plane they're on, and where that plane stands in relation to the rest of the multiverse. They have to know that their spells aren't infallible, and that their magic will never have the same effect twice. But that's the price mages pay for the power at their command.
==Dimensional Relations==
The planes are all interrelated. The Ethereal connects all of the Inner Planes as well as the Prime, but doesn't touch the Outer Planes. None of the Inner Planes has a direct connection to any of the Outer Planes, but they do have metaphysical contact with each other. Similarly, the Outer Planes are related by proximity or the Astral Plane, which also reaches the Prime.
A wizard has to note these connections when he casts certain spells. Few prime wizards ever think about it, but a number of their common spells require a link to one or more of the various planes. If cast on a plane where that link isn't possible, the spell fails. It's as simple as that.
It's easy enough to figure if these links—also called planar pathways—are accessible or not. Think of it this way: All of the planes belong to one of two groups, the Ethereal group and the Astral group. The Ethereal group comprises the Inner Planes, along with the Ethereal and the Prime. The Astral group includes the first layer of each Outer Plane, the Astral, and the Prime. Only the Prime Material Plane exists in both groups—that's why almost all spells work there. Spells requiring connections to planes outside of the group a mage currently inhabits cannot work. No planar pathway exists from Ysgard to the Demiplane of Shadow, so spells utilizing shadow magic just don't function on Ysgard. Likewise, a body can't conjure a baku from the Outlands to the plane of Radiance—a restriction that obeys both the Dimensional Relations rule and the general rule about planar summonings.
A few spells (listed in the "Dual" category in the table below) reach through either the Astral or the Ethereal, depending on where the spell is cast. Contact other plane, for example, reaches through the Astral to the Outer Planes and through the Ethereal to the Inner. A wizard on the plane of Fire hoping for an answer from a creature of Gehenna gets nothing but static.
Related to this concept is the existence of extradimensional spaces. These small pockets of space are located in hidden dimensions beyond normal perception. Certain spells, as noted in the table below, access or create extradimensional spaces to achieve their effects. The Astral Plane, due to its nature, doesn't have extra dimensions. Thus, there's nowhere for a maze spell to send its victim, and no place for rope trick to create its hidden room. A few Ethereal demiplanes are also rumored to be cut off from extradimensional space.
Remember, just because the wizard's normally cut off from these spells doesn't mean he can never cast them; with spell keys (explained below), most any spell can be restored to its full function.
==Alterations By School==
Wizards must also deal with the changes that occur to the various types, or schools, of magic on certain planes. Mages need to be mindful of the schools from which they draw their spells, not forgetting that many fall in two or more schools. The commonly used fireball, for example, is both an evocation and an elemental fire spell.
Each plane has its own set of physical laws and interactions with the forces of magic. Certain types of magic can be nulled, enhanced, diminished, or simply altered. The table on page 107 shows the general modifications to each spell school on each plane, but the actual changes vary as much as the planes themselves. The Dungeon Master can find complete information for each Outer Plane's magical changes in the Planes of Chaos, Planes of Law, and Planes of Conflict boxed sets.
In general, though, the following conditions apply.
Null means that certain spells simply don't work on a given plane. These are usually based on elemental or philosophical opposites. For example, water spells never work on the plane of Fire. Certain "null" spells may be restored with spell keys, such as wild magic on Mechanus.
Diminished spells function at one level lower than normal. This occurs when a plane's composition and physics aren't conducive to that particular school of magic, but not to such a degree that the spells cannot function at all. For example, elemental fire spells are diminished on the plane of Earth, so a fireball spell cast by a 5th-level mage there inflicts only 4d6 points of damage. ln addition, spells higher than 4th level cannot be cast at all by anyone.
Enhanced spells always function as though cast by a wizard one level higher than the caster's actual level. This happens on planes where that type of spell is conducive to the environment due to similarity or general fostering of such effects; for example, violent invocations and evocations on Gehenna mirror the violence of the plane. Thus, a fireball spell cast by a 5th-level mage inflicts 6d6 points of damage, and the target's saving throw is made with a -1 penalty. Spells that provide protection gain a + 1 bonus, so a fire shield cast on Gehenna grants the wizard a +J saving throw bonus versus cold-based attacks (rather than +2).
Alterations are by far the most common changes to spells, and their effects vary so much it's impossible to catalogue them here. Spells so changed by the plane can manifest in a number of different ways. These effects shift from plane to plane and spell to spell, but some consistent patterns exist: For example, all fire spells on the plane of Ice produce explosions of steam rather than fire. Sometimes only the appearance of the spell's effect changes, while other times, the general nature of the spell itself changes. On some planes, spells change to their opposite in effect or intent. On Mount Celestia, for example, death magic always reflects back upon the caster. Or the reliability of the magic itself may diminish, making any attempt at spellcasting an unsure proposition — like casting alteration school spells in the Abyss.
==Spell Keys==
Spell keys allow a wizard to bypass some of the above restrictions. See, it's possible to learn the particulars of a plane's alterations and adapt spellcasting to those conditions. Spell keys enable a wizard to cast spells so that they function normally on planes where such magic is altered or even completely ineffective, whether the limitation's due to a planar pathway restriction or a school alteration. They do this by "attuning" a wizard's spells to the magical vibrations of a given plane.
These keys must be added to the incantations, gesticulations, or required material components used to cast a spell. As extra requirements, virtually all spell keys add at least 1 to the casting time of the spell with which they're used.
Spell keys take different forms depending on where they're required. For example, on Ysgard spell keys are runes that are traced in the air or spoken aloud. On Mechanus they take the form of mathematical formulae traced on tiny cogs. On Limbo they constantly change, reflecting that plane's chaotic nature.
Some spell keys prove far more useful than others to a spellslinger. General keys allow a cutter to effectively cast any spell from a group of spells, while specific keys only affect one particular spell. A general key might restore all of the spells of a particular school of magic — such as conjuration/summoning spells on Baator — while another key might affect all wall-related spells on Limbo. A specific spell key would only restore invisibility on Arcadia or power word: kill on Mount Celestia, for example.
Planar mages know the dark of spell keys and constantly look for new ones. There isn't a spell key for every spell or school that suffers alterations, however. The Planar Absolutes table on page 107 shows unconditional spellcasting prohibitions on the planes. Some spells simply won't work on certain planes, no matter what a body does.
Current chant says that some bashers have developed or discovered a new type of spell key that affects other plane-based limitations. It's said that some of these keys allow a monster summoning spell to call forth creatures from nonadjacent planes, while others extend the ranges of certain spells so that they can be cast across planar distances when they could not before. Some even say that there're spell keys that'll let a cutter cast a spell through an open portal.
==Table 2: School Alterations by Plane==
PLANE 	ABJ	ALT	CON/SUM	DIV	ENC/CHA	ILL/PHA	INV/Evo	NEC	WIL	ELEMENTAL	ELEMENTAL	ELEMENTAL	ELEMENTAL
PLANE 	ABJ	ALT	CON/SUM	DIV	ENC/CHA	ILL/PHA	INV/Evo	NEC	WIL	A 	F 	E 	W
Astral 	— 	✦ 	> 	— 	— 	— 	— 	— 	— 	✦ 	✦ 	✦ 	✦
Ethereal 	> 	— 	✦ 	∴ 	— 	— 	— 	— 	— 	— 	— 	✦ 	✦
Elemental: Air 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	+ 	> 	> 	>
Elemental: Earth	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	> 	> 	+ 	>
Elemental: Fire 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	> 	+ 	> 	∴
Elemental: Water	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	> 	∴ 	> 	+
PE: Ice 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	— 	> 	> 	—
PE: Magma 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	> 	— 	— 	∴
PE: Ooze 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	> 	> 	— 	—
PE: Smoke 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	— 	— 	> 	>
QE: Lightning 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	+ 	— 	> 	✦
QE: Mineral 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	> 	> 	+ 	✦
QE: Radiance 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	— 	+ 	— 	>
QE: Steam 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	+
Positive Energy 	— 	— 	✦ 	— 	— 	— 	✦ 	✦ 	+ 	— 	+ 	✦ 	✦
Negative Energy 	— 	— 	✦ 	— 	— 	— 	✦ 	✦ 	> 	> 	> 	✦ 	✦
QE: Ash 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	✦ 	∴ 	— 	✦
QE: Dust 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	✦ 	— 	— 	>
QE: Salt 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	— 	— 	— 	∴
QE: Vacuum 	— 	— 	✦ 	— 	— 	— 	✦ 	— 	— 	∴ 	∴ 	— 	—
Abyss 	— 	✦ 	✦ 	✦ 	— 	+ 	— 	✦ 	+ 	✦ 	✦ 	✦ 	✦
Acheron 	— 	— 	✦ 	✦ 	— 	— 	— 	✦ 	> 	✦ 	✦ 	✦ 	✦
Arborea 	— 	— 	✦ 	✦ 	✦ 	— 	— 	✦ 	— 	✦ 	✦ 	✦ 	✦
Arcadia 	— 	— 	✦ 	✦ 	✦ 	✦ 	— 	✦ 	> 	✦ 	✦ 	✦ 	✦
Baator 	— 	— 	✦ 	✦ 	— 	— 	— 	✦ 	> 	✦ 	✦ 	✦ 	✦
Beastlands 	— 	✦ 	✦ 	✦ 	✦ 	— 	— 	✦ 	— 	✦ 	✦ 	✦ 	✦
Bytopia 	— 	— 	✦ 	✦ 	— 	— 	— 	✦ 	— 	✦ 	✦ 	✦ 	✦
Carceri 	— 	✦ 	✦ 	✦ 	— 	— 	— 	✦ 	— 	✦ 	✦ 	✦ 	✦
Elysium 	— 	— 	✦ 	✦ 	✦ 	— 	— 	✦ 	— 	✦ 	✦ 	✦ 	✦
Gehenna 	— 	— 	✦ 	✦ 	> 	— 	+ 	✦ 	— 	✦ 	✦ 	✦ 	✦
Gray Waste 	— 	— 	✦ 	✦ 	✦ 	— 	— 	✦ 	— 	✦ 	✦ 	✦ 	✦
Limbo 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦
Mechanus 	— 	— 	✦ 	✦ 	— 	∴ 	— 	✦ 	∴ 	✦ 	✦ 	✦ 	✦
Mount Celestia 	— 	— 	✦ 	✦ 	— 	— 	— 	✦ 	> 	✦ 	✦ 	✦ 	✦
Outlands 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦ 	✦
Pandemonium 	— 	✦ 	✦ 	✦ 	— 	— 	— 	✦ 	+ 	✦ 	✦ 	✦ 	✦
Ysgard 	— 	✦ 	✦ 	✦ 	— 	— 	— 	✦ 	+ 	✦ 	✦ 	✦ 	✦
: — No alteration to school.
: ✦ Alterations to school occur; the spell may need help to work, or its effects may be changed.
: > School is diminished on plane.
: + School is enhanced on plane.
: ∴ School is null on plane. All spells of that school simply do not function. It may be possible to restore them with spell keys.
Note: Spell keys may allow spells to function normally. Most keys add 1 to the initiative or casting time of the spell.
==Table 3: Planar Absolutes (Absolute Prohibitions of Magic by Plane)==
For both wizards and priests, the following schools or types of spells never function on the noted plane, even with spell or power keys.
Otherwise, even spell types noted as "null" above can be restored with keys.
Plane 	Absolute Restriction
Elemental Fire 	No water spells
Elemental Water	No fire spells*
PE: Magma 	No water spells
QE: Vacuum 	No air spells
Outlands 	Special by ring**
Sigil 	No interplanar transport spells (gate, plane shift, teleport without error, and so on)
: * Unless the spell is cast within an elemental pocket or other distinct environment. For example, a fireball ~ be cast on the plane of
Water within the confines of the City of Glass or in an air bubble. (Note that even within an air bubble on the planes of Fire or
Magma, the temperatures remain too high to tolerate water spells.)
: ** As noted on page 10, magic that can be cast on the Outlands depends on where a cutter stands. Within the 7th ring, for example,
8th- and 9th-level spells simply cannot function. Right next to the Spire, all magic is completely annulled. A complete guide to these
conditions is available in A Player's Primer to the Outlands (261O).