Traps

Traps can be found almost anywhere. One wrong step in an ancient tomb might trigger a series of scything blades, which cleave through armor and bone. The seemingly innocuous vines that hang over a cave entrance might grasp and choke anyone who pushes through them. A net hidden among the trees might drop on travelers who pass underneath. In a  fantasy game, unwary adventurers can fall to their deaths, be burned alive, or fall under a fusillade of poisoned darts.

A trap can be either mechanical or magical in nature. Mechanical traps include pits, arrow traps, falling blocks, water-filled rooms, whirling blades, and anything else that depends on a mechanism to operate. Magic traps are either magical device traps or spell traps. Magical device traps initiate spell effects when activated. Spell traps are spells such as Glyph of Warding and symbols that function as traps.

***Traps in Play***

When adventurers come across a trap, you need to know how the trap is triggered and what it does, as well as the possibility for the characters to detect the and to disable or avoid it.

***Triggering a Trap***

Most traps are triggered when a creature goes somewhere or touches something that the trap’s creator wanted to protect. Common triggers include stepping on a pressure plate or a false section of floor, pulling a tripwire, turning a doorknob, and using the wrong key in a lock. Magic traps are often set to go off when a creature enters an area or touches an object. Some magic traps (such as the Glyph of Warding spell) have more complicated trigger conditions, including a password that prevents the trap from activating.

***Detecting and Disabling a Trap***

Usually, some element of a trap is visible to careful inspection. Characters might notice an uneven flagstone that conceals a pressure plate, spot the gleam of light off a tripwire, notice small holes in the walls from which jets of flame will erupt, or otherwise detect something that points to a trap’s presence.

A trap’s description specifies the checks and DCs needed to detect it, disable it, or both. A character actively looking for a trap can attempt a Perception (Int) check against the trap’s DC. You can also compare the DC to detect the trap with each character’s Perception (Com) check to determine whether anyone in the party notices the trap in passing. If the adventurers detect a trap before triggering it, they might be able to disarm it, either permanently or long enough to move past it. You might call for an Investigation check for a character to deduce what needs to be done, followed by a Dexterity check using thieves’ tools, or something that can act like thieves’ tools, to perform the necessary sabotage.

Any character can attempt an Occult (Cun) check to detect or disarm a magic trap, in addition to any other checks noted in the trap’s description. The DCs are the same regardless of the check used. In addition, Dispel Magic has a chance of disabling most magic traps. A magic trap’s description provides the DC for the ability check made when you use Dispel Magic.

In most cases, a trap’s description is clear enough that you can adjudicate whether a character’s actions locate or foil the trap. As with many situations, you shouldn’t allow die rolling to override clever play and good planning. Use your common sense, drawing on the trap’s description to determine what happens. No trap’s design can anticipate every possible action that the characters might attempt.

You should allow a character to discover a trap without making an ability check if an action would clearly reveal the trap’s presence. For example, if a character lifts a rug that conceals a pressure plate, the character has found the trigger and no check is required.

Foiling traps can be a little more complicated. Consider a trapped treasure chest. If the chest is opened without first pulling on the two handles set in its sides, a mechanism inside fires a hail of poison needles toward anyone in front of it. After inspecting the chest and making a few checks, the characters are still unsure if it’s trapped. Rather than simply open the chest, they prop a shield in front of it and push the chest open at a distance with an iron rod. In this case, the trap still triggers, but the hail of needles fires harmlessly into the shield.

Traps are often designed with mechanisms that allow them to be disarmed or bypassed. Intelligent creatures that place traps in or around their lairs need ways to get past those traps without harming themselves. Such traps might have hidden levers that disable their triggers, or a secret door might conceal a passage that goes around the trap.

***Trap Effects***

The effects of traps can range from inconvenient to deadly, making use of elements such as arrows, spikes, blades, poison, toxic gas, blasts of fire, and deep pits. The deadliest traps combine multiple elements to kill, injure, contain, or drive off any creature unfortunate enough to trigger them. A trap’s description specifies what happens when it is triggered.

The attack bonus of a trap, the save DC to resist its effects, and the damage it deals can vary depending on the trap’s severity. Use the trap save DCs and attack bonuses table and the damage severity by level table for suggestions based on three levels of trap severity.

A trap intended to be a setback is unlikely to kill or seriously harm characters of the indicated levels, whereas a dangerous trap is likely to seriously injure (and potentially kill) characters of the indicated levels. A deadly trap is likely to kill characters of the indicated levels.

*Trap Save DCs and Attack Bonuses*

Trap Danger         Save DC     Attack Bonus

Setback         10–11         +3 to +5

Dangerous         12–15         +6 to +8

Deadly         16–20         +9 to +12

*Damage Severity by Level*

Character Level     Setback     Dangerous     Deadly

1st–4th         1d10         2d10         4d10

5th–10th         2d10         4d10         10d10

11th–16th         4d10         10d10         18d10

17th–20th         10d10         18d10         24d10

***Complex Traps***

Complex traps work like standard traps, except once activated they execute a series of actions each round. A complex trap turns the process of dealing with a trap into something more like a combat encounter. When a complex trap activates, it rolls initiative. The trap’s description includes an initiative bonus. On its turn, the trap activates again, often taking an action. It might make successive attacks against intruders, create an effect that changes over time, or otherwise produce a dynamic challenge. Otherwise, the complex trap can be detected and disabled or in the usual ways.

For example, a trap that causes a room to slowly flood works best as a complex trap. On the trap’s turn, the water level rises. After several rounds, the room is completely flooded.

***Sample Traps***

The magical and mechanical traps presented here vary in deadliness and are presented in alphabetical order.

***Collapsing Roof***

*Mechanical Trap*

This trap uses a tripwire to collapse the supports keeping an unstable section of a ceiling in place. The tripwire is 10 cm off the ground and stretches between two support beams. The DC to spot the tripwire is 10. A successful DC 15 Dexterity check using thieves’ tools disables the trip wire harmlessly. A character without thieves’ tools can attempt this check with disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.

Anyone who inspects the beams can easily determine that they are merely wedged in place. As an action, a character can knock over a beam, causing the trap to trigger. The ceiling above the tripwire is in bad repair, and anyone who can see it can tell that it’s in danger of collapse.

When the trap is triggered, the unstable ceiling collapses. Any creature in the area beneath the unstable section must succeed on a DC 15 Dexterity saving throw, taking 22 (4d10) bludgeoning damage on a failed save, or half as much damage on a successful one. Once the trap is triggered, the floor of the area is filled with rubble and becomes difficult terrain.

***Falling Net***

*Mechanical Trap*

This trap uses a tripwire to release a net suspended from the ceiling. The tripwire is 10 cm off the ground and stretches between two columns or trees. The net is hidden by cobwebs or foliage. The DC to spot the tripwire and net is 10. A successful DC 15 Dexterity check using thieves’ tools breaks the trip wire harmlessly. A character without thieves’ tools can attempt this check with disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.

When the trap is triggered, the net is released, covering a 2-m-square area. Those in the area are trapped under the net and restrained, and those that fail a DC 10 Brawn saving throw are also knocked prone. A creature can use its action to make a DC 10 Brawn check, freeing itself or another creature within its reach on a success. The net has AC 10 and 20 hit points. Dealing 5 slashing damage to the net (AC 10) destroys a 1 m square section of it, freeing any creature trapped in that section.

***Fire-Breathing Statue***

*Magic Trap*

This trap is activated when an intruder steps on a hidden pressure plate, releasing a magical gout of flame from a nearby statue. The statue can be of anything, including a dragon or a mage casting a spell.

The DC is 15 to spot the pressure plate, as well as faint scorch marks on the floor and walls. A spell or other effect that can sense the presence of magic, such as Detect Magic, reveals an aura of evocation magic around the statue.

The trap activates when more than 10 kg of weight is placed on the pressure plate, causing the statue to release a 6 m cone of fire. Each creature in the fire must make a DC 13 Dexterity saving throw, taking 22 (4d10) fire damage on a failed save, or half as much damage on a successful one.

Wedging an iron spike or other object under the pressure plate prevents the trap from activating. A successful Dispel Magic (DC 13) cast on the statue destroys the trap.

***Pits***

*Mechanical Trap*

Four basic pit traps are presented here:

***Simple Pit***: A simple pit trap is a hole dug in the. The hole is covered by a large cloth anchored on the pit’s edge and camouflaged with dirt and debris. The DC to spot the pit is 10. Anyone stepping on the cloth falls through and pulls the cloth down into the pit, taking damage based on the pit’s depth (usually 3 m, but some pits are deeper).

***Hidden Pit***: This pit has a cover constructed from material identical to the floor around it. A successful DC 15 Perception (Int) check discerns an absence of foot traffic over the section of the floor that forms the pit’s cover. A successful DC 15 Investigation check is necessary to confirm that the trapped section of the floor is actually the cover of a pit.

When a creature steps on the cover, it swings open like a trapdoor, causing the intruder to spill into the pit below. The pit is usually 3 or 5 m deep but can be deeper. Once the pit trap is detected, an iron spike or similar object can be wedged between the pit’s cover and the surrounding floor in such a way as to prevent the cover from opening, thereby making it safe to cross. The cover can also be magically held shut using the Arcane Lock spell or similar magic.

***Locking Pit***: This Pit trap is identical to a hidden Pit trap, with one key exception: the trap door that covers the Pit is spring-loaded. After a creature falls into the Pit, the cover snaps shut to trap its victim inside.

A successful DC 20 Brawn check is necessary to pry the cover open. The cover can also be smashed open. A character in the pit can also attempt to disable the spring mechanism from the inside with a DC 15 Dexterity check using thieves’ tools, provided that the mechanism can be reached and the character can see. In some cases, a mechanism (usually hidden behind a secret door nearby) opens the pit.

***Spiked Pit***: This pit trap is a simple, hidden, or locking pit trap with sharpened wooden or iron spikes at the bottom. A creature falling into the pit takes 11 (2d10) piercing damage from the spikes, in addition to any falling damage. Even nastier versions of poison smeared on the spikes. In that case, anyone taking piercing damage from the spikes must also make a DC 13 Vitality saving throw, taking a 22 (4d10) poison damage on a failed save, or half as much damage on a successful one.

***Poison Darts***

*Mechanical Trap*

When a creature steps on a hidden pressure plate, poison-tipped darts shoot from spring-loaded or pressurized tubes cleverly embedded in the surrounding walls. An area might include multiple pressure plates, each one rigged to its own set of darts.

The tiny holes in the walls are obscured by dust and cobwebs, or cleverly hidden amid bas-reliefs, murals, or frescoes that adorn the walls. The DC to spot them is 15. With a successful DC 15 Investigation check, a character can deduce the presence of the pressure plate from variations in the mortar and stone used to create it, compared to the surrounding floor. Wedging an iron spike or other object under the pressure plate prevents the trap from activating. Stuffing the holes with cloth or wax prevents the darts contained within from launching.

The trap activates when more than 10 kg of weight is placed on the pressure plate, releasing four darts. Each dart makes a ranged attack with a +8 bonus against a random target within 2 m of the pressure plate (vision is irrelevant to this attack roll). (If there are no targets in the area, the darts don’t hit anything.) A target that is hit takes 2 (1d4) piercing damage and must succeed on a DC 15 Vitality saving throw, taking 11 (2d10) poison damage on a failed save, or half as much damage on a successful one.

***Poison Needle***

*Mechanical Trap*

A poisoned needle is hidden within a treasure chest’s lock, or in something else that a creature might open. Opening the chest without the proper key causes the needle to spring out, delivering a dose of poison.

When the trap is triggered, the needle extends 10 cm straight out from the lock. A creature within range takes 1 piercing damage and 11 (2d10) poison damage, and must succeed on a DC 15 Vitality saving throw or be poisoned for 1 hour. A successful DC 20 Investigation check allows a character to deduce the trap’s presence from alterations made to the lock to accommodate the needle. A successful DC 15 Dexterity check using thieves’ tools disarms the trap, removing the needle from the lock. Unsuccessfully attempting to pick the lock triggers the trap.

***Rolling Sphere***

*Mechanical Trap*

When 10 or more kg of pressure are placed on this trap’s pressure plate, a hidden trapdoor in the ceiling opens, releasing a 2 m diameter rolling sphere of solid stone.

With a successful DC 15 Perception (Int) check, a character can spot the trapdoor and pressure plate. A search of the floor accompanied by a successful DC 15 Investigation check reveals variations in the mortar and stone that betray the pressure plate’s presence. The same check was made while inspecting the ceiling notes variations in the stonework that reveal the trapdoor. Wedging an iron spike or other object under the pressure plate prevents the trap from activating.

Activation of the sphere requires all creatures present to roll Initiative. The sphere rolls initiative with a +8 bonus. On its turn, it moves 12 m in a straight line. The sphere can move through creatures’ spaces, and creatures can move through its space, treating it as difficult terrain. Whenever the sphere enters a creature’s space or a creature enters its space while it’s rolling, that creature must succeed on a DC 15 Dexterity saving throw or take 55 (10d10) bludgeoning damage and be knocked prone. The sphere stops when it hits a wall or a similar barrier. It can’t go around corners, but smart dungeon builders incorporate gentle, curving turns into nearby passages that allow the sphere to keep moving.

As an action, a creature within 1 m of the sphere can attempt to slow it down with a DC 20 Brawn check. On a successful check, the sphere’s speed is reduced by 3 m. If the sphere’s speed drops to 0, it stops moving and is no longer a threat.

***Sphere of Annihilation***

*Magic Trap*

Magical, impenetrable darkness fills the gaping mouth of a stone face carved into a wall. The mouth is 0.5 m in diameter and roughly circular. No sound issues from it, no light can illuminate the inside of it, and any matter that enters it is instantly obliterated.

A successful DC 20 Occult (Int) check reveals that the mouth contains a Sphere of Annihilation that can’t be controlled or moved. It is otherwise identical to a normal Sphere of Annihilation.

Some versions of the trap include an enchantment placed on the stone face, such that specified creatures feel an overwhelming urge to approach it and crawl inside its mouth. This effect is otherwise like the Sympathy aspect of the Antipathy/Sympathy spell. A successful Dispel Magic (DC 18) removes this enchantment.