A trap can be either mechanical or magic in nature. Mechanical traps fall can be simple or complex. Magical traps can be created like magic items or cast using spells. The type of trap determines a lot about how it can be created, detected, and disarmed.
Simple traps (snares, pits, traps made from natural elements such as falling logs) can be detected with an Investigation check made against the trap's DC. They are also easier to disarm, and most can obviously be disarmed without a skill check (i.e. a pit can simply be uncovered). If the GM decides that a traps check makes sense, you get advantage on it. For some simple traps, the GM may even allow you to set it with a Dex check.
Complex mechanical traps are usually well-hidden and difficult to disable, and so they require extra training. A traps check is necessary to create, find, or disable these.
A magical trap functions like a magic item that stores a spell and automatically releases it when triggered. As magic items, they are crafted in advance, they can be detected with detect magic, and their effects can temporarily be suppressed for 1d4 rounds with a dispel magic spell. Magical traps can also be detected and disabled with successful traps checks. To craft a magic trap you must have the create magical traps proficiency and be able to cast the relevant spells. When crafting these traps, you can also choose to use your magic items skill instead of your traps skill.
Spell traps are simply created by casting the appropriate spell. They function as spells and don't require any extra proficiency to create. They are often cheaper, as well.
Elements of a Trap
All traps--mechanical or magic--have the following elements: trigger, reset, DC, effect, and Challenge Rating. Some traps may also include optional elements, such as poison or a bypass. These characteristics are described below.
Trigger
A trap's trigger determines how it is sprung.
Location: A location trigger springs a trap when someone stands in a particular place.
Proximity: This trigger activates the trap when a creature approaches within a certain distance of it. Flying creatures set off proximity triggers, but they don't set off location triggers. Proximity traps add 1,000 gp to the cost of a trap.
Sound: This trigger springs a magic trap when it detects any sound. A sound trigger functions like an ear and has a +15 circumstance bonus on Perception checks.
Visual: This trigger for magic traps works like an actual eye, springing the trap whenever it "sees" something. These can be fooled by darkness, invisibility, or other tricks.
Touch: A touch trigger springs the trap when touched.
Reset
A reset element is the set of conditions under which a trap becomes ready to trigger again.
No Reset: Short of completely rebuilding the trap, there's no way to trigger it more than once.
Repair: To get the trap functioning again, you must repair it. Doing so requires a traps check and material worth 1/5 the trap's price.
Manual: Resetting the trap requires someone to move the parts back into place. This is the kind of reset element most mechanical traps have. In most cases, manual resets require 1 minute of time and are simple enough to not require a skill check.
Automatic: The trap resets itself, either immediately or after a timed interval.
Trap DC
All traps have a DC that determines how hard it is to find, disarm, avoid damage from, or bypass the traps. All traps can be intentionally set off instead of disarming them. Unless you are familiar with the exact workings of a particular traps, this can be a dangerous decision, though.
Effect
The effect of a trap is what happens to those who spring it. Usually this takes the form of either damage or a spell effect, but some traps have special effects. Traps may be pits you fall into (5 points of damage per 10 feet of depth), they may fling or shoot objects at you, they may trigger spell effects, or hit you with items.
A trap usually either makes an attack roll or forces a saving throw to avoid it. Some traps never miss and don't have a way to avoid damage. These traps usually have an onset of a few rounds during which time players need to realize they are in danger and take appropriate steps to avoid it.
Price
A trap's price indicates how much you would spend to buy it on the open market. Crafting traps usually costs half the market price.
Enhancements
There are a number of ways that traps can be enhanced. Below are a few of the most common.
Bypass: A bypass allows you to temporarily disable a mechanical trap without completely disarming it. Bypasses may be locks or hidden switches. In most cases, the lock's DC is used to find hidden bypasses or pick bypass locks. Bypasses cost an extra 200 gp.
Extra Darts: Dart traps can sometimes be designed to double the number of darts shot at victims. This increases the number of darts to 1d8 per person, +1 CR, and +500 gp.
Extra Spears: Spear traps can fire multiple spears. Each spear makes a separate attack, adds 500 gp to the price, and +1 to the CR.
Improved Power: For melee traps, this increases the force behind the objects trajectory, boosting the damage done. Each upgrade adds: +1 damage (max +8) and 100 gp.
Improved Quality: Traps with higher quality are harder to find and disable. Each upgrade adds: +1 DC, +200 gp.
Improved Targeting: Improved targeting makes traps that attack easier to hit their victims. Each upgrade to targeting adds: +1 CR, +5 attack, and +1,000 gp.
Increased Weight: Some traps rely on weight of objects to crush targets. Each increment of increased weight adds: +1 CR, 2d6 bludgeoning damage, DC +2, and +2,500 gp.
Poison: Adding a poison (usually an injury poison) can boost your trap's effectiveness beyond the simple wounds it inflicts. Poisons increase the CR of a trap by the CR of the poison itself. The price of the trap also increases by the price of the poison.
Proximity Trigger: As described above, most mechanical traps require the pushing of a pressure plate or some other sensor to activate them. Proximity triggers, however, simply require you to approach the trap within a certain distance. While used on mechanical traps, these triggers are often semi-magical in nature, using spells like alarm to create their effect. Proximity triggers add 1,000 gp to the cost of a trap.
Spikes: Spikes can be added to some traps to increase damage. In traps that involve falling (pit traps), spikes add extra piercing damage on top of fall damage. When creatures fall, make an +10 melee attack for 1d4 spikes. Each does 1d4+2 piercing damage (in addition to the normal fall damage). Spikes increase the CR of the trap by 1 and increases the price by 500 gp.
Sample Traps
Arrow Trap
As its name implies, an arrow trap involves shooting an arrow at a creature that sets it off. In its most basic form, the arrow trap is just a tripwire attached to a crossbow, though the trap may be augmented with more sophisticated triggers, poisons, hidden arrow launchers, and other improvements. Almost all arrow traps require manual reset and the effort of hiding a projectile device in a way that is not noticeable, something that makes arrow traps one of the easier traps to avoid.
Type: complex mechanical (simple mechanical if triggered by a rudimentary tripwire)
Trigger: Any
Reset: Manual
DC: 20 CR: 1
Effect: +10 ranged attack. Damage from arrow or bolt (1d4 - 1d8)
When triggered, a blade trap sweeps a blade at the target, making a melee attack. The blade may be a scythe, dagger, sword, or another blade-like object. The blade may swing out of a wall, the floor, the ceiling, a chest, or any other fixed object. Because blade emerging from solid surfaces are difficult to conceal these traps often are difficult to hide and easier to spot than some, though that doesn't make them any less deadly.
Type: complex mechanical
Trigger: Any
Reset: automatic
DC: 21 CR: 1
Effect: When triggered, the traps makes a +10 melee attack. If successful, the blade deals 1d8 or 1d10 points of slashing damage.
One of the simplest traps involves smearing a contact poison on a commonly touched surface, like a doorknob or lock. Most contact poisons are nearly invisible to sight and very hard to detect. As simple traps, they can be detected with a basic perception, poison, or traps checks. They can also be applied using a poison check instead of a traps check. Disarming them requires careful attention to be able to remove all the residue without accidental poisoning, though some clever creatures may think of creative ways to avoid touching the trapped surface.
Type: simple (poison)
Trigger: Touch
Reset: none
DC: 25 CR: The CR of the poison
Effect: The effect of the poison
Price: The cost of the poison
Enhancements: None
Crushing Room Trap
Crushing room traps are difficult to spot, hard to escape, and almost always dangerous. When triggered, a part of the room slowly closes in, crushing those in between. The crushing surface may be a wall, multiple walls, the ceiling, or even just a part of the room. Crushing rooms always reset automatically and usually have a bypass of some sort.
Type: complex mechanical
Trigger: location
Reset: automatically
DC: 22 CR: 10
Effect: All targets in the area under the crushing surface are affected without fail if they are caught when the walls go off. The walls may close in slowly or crush suddenly. Walls that crush suddenly typically have a 2-round delay after triggered before slamming closed. Any targets caught in the crushing area suffer 16d6 bludgeoning damage.
Price: 29,000 gp
Enhancements: Bypass
Dart Traps
When one of these traps is triggered, a flurry of darts flies your direction. Dart traps are smaller and easier to hide than arrows or spears, but they can do less damage. A little poison added to the darts can make them considerably more dangerous, though. Dart traps can also target multiple people if they are all adjacent to the trap's trigger.
Type: complex mechanical
Trigger: location
Reset: manual
DC: 20 CR: 1
Effect: Fires 1d4 darts at each target in two adjacent squares near the trigger. Each dart attacks at +10 and does 1d4+1 damage.
Price: 500 gp
Enhancements: Bypass, Extra darts, Improved Targeting, Improved Quality, Poison
Falling Block Trap
These traps are designed to drop a heavy object on you when you trigger it. Often this is just bricks or blocks from the ceiling. Because these kinds of trap require collapsing a large part of the surrounding structure, resetting them usually requires repairing the surrounding tunnel or building itself.
Type: complex mechanical
Trigger: Any
Reset: repair
DC: 22 CR: 2
Effect: Any targets in two adjacent 5' squares suffer 2d6 bludgeoning damage. A dex save (DC 22) negates this damage.
This is a classic room trap. The exits to a room are blocked in some way and the room rapidly starts filling up with water, eventually drowning anyone in it.
Type: complex mechanical
Trigger: Location or Proximity (+1,000 gp)
Reset: manual or automatic (+500 gp)
DC: 22 CR: 4
Effect: The entrances to the room immediately shut in some way (at GM's discretion) and the room begins to flood, a process which takes only 5 rounds. To exit the room, the door must be opened (locks check), a secret passage must be found (investigation), or some sort of puzzle completed. Regardless of how an escape is managed, the skill checks required to do so are a DC 22.
Price: 11,200 gp
Enhancements: The flooding room trap can be upgraded to a CR 5 (4 rounds, DC 23) or CR 7 (3 rounds, DC 25). Each upgrade adds an additional 5,000 gp to the price.
Magical Traps
Magical traps are traps that mimic the effects of a common magic spells. Because they don't use a physical mechanism, magic traps are much more difficult to find and disarm. However, magical traps function as magic items, so they can be detected with a detect magic spell. A dispel magic spell doesn't disable a magical trap, but it does suppress it for 1d4 rounds.
Type: magic
Trigger: Any
Reset: none, automatic (price x 10)
DC: 25+Spell Level CR: Spell level of the highest spell
Effect: As per the spell's effects. Many spells can be turned into magical traps, but the following are the most common: Burning Hands, Inflict, Ghoul Touch, , Acid Arrow, Bestow Curse, Lightning Bolt, Fireball, Phantasmal Killer, Flame Strike, Chain Lightning, Black Tentacles, Summon Monster, Blade Barrier, Destruction , Earthquake, Power Word Stun, Prismatic Spray , Reverse Gravity, Incendiary Cloud, Enervation
Price: See scroll creation cost
Enhancements: Spells can be improved using metamagic techniques, but the increased spell level counts toward the price, DC, and CR. A proximity trigger can be added to these traps.
Pit Traps
A pit trap is very simple. You dig a big pit in the ground, hide it, and hope someone falls in it. Spikes, poison, and nasty creatures can be added to the trap to make it a bit more effective.
Type: simple mechanical
Trigger: Location
Reset: manual (re-hiding the pit)
DC: 20 CR: 1 CR for every 10 feet deep.
Effect: Dex save avoids. Fall damage depending on the depth of the pit.
Price: 1,000 gp per 10 feet of depth
Enhancements: Poison (requires spikes), Spikes. Various other items (acid, water, creatures, traps) can be put at the bottom of the pit. It's best to calculate the cost and CR of these additions as if they were separate encounters.
Poison Needle Traps
A poison needle trap usually guards a lock, check, doorknob, or another item that is likely to be grabbed. When the trapped object is touched, the needle is sprung, piercing the target's hand and delivering an injury-based poison.
Type: complex mechanical
Trigger: Touch
Reset: Manual, Automatic (+500 gp), or Repair (-200 gp)
DC: 20 CR: The CR of the poison
Effect: Dex save negates. If failed, the target takes 1 hp of damage and must save versus the poison's effect.
Price: 1,000 gp + The cost of the poison
Enhancements: Bypass, Improved Quality, Poison
Spear Traps
Similar to arrow traps, the spear trap shoots a projectile at its target when triggered, only these traps shoot spears not arrows. Like arrow traps, spear traps can sometimes be difficult to hide.
Type: complex mechanical
Trigger: All
Reset: Manual
DC: 20 CR: 1
Effect: +10 ranged attack. Damage from spear (1d8 piercing).
Some spells are designed to create traps. These spells function exactly as written. As spells they can be detected by detect magic and they can usually be disabled by dispel magic.
Type: magic
Trigger: varies
Reset: varies
DC: Your save DC CR: Spell Level
Effect: Per the spell. See Fire Trap, Glyph of Warding, Sepia Snake Sigil, etc.
Price: material component cost
Enhancements: varies
Trap Door
A trap door functions as a pit traps with some functional variations. Generally, trap doors are harder to spot and disarm, and can reset automatically.
Type: complex mechanical
Trigger: Location
Reset: automatic
DC: 25 CR: 1 CR + 1 for every 10 feet deep.
Effect: Dex save avoids. Fall damage depending on the depth of the pit.
Vapor traps are designed to release a cloud of inhalable poison gas. Usually only one dose of poison gas is loaded into such traps at a time and so aren't resettable. The gas fills a 10x10 foot area (4 squares) affecting all breathing creatures who are standing in it.
Type: complex mechanical
Trigger: location
Reset: none
DC: DC of the poison CR: CR of the poison
Effect: see poison
Price: price of the poison
Enhancements: Bypass, Poison
Misc. Traps
Bear Trap
This trap features a spiked clamp that slams shut on anyone stepping on it. The entire trap itself is usually hidden and can be attached to a wall or tree by a chain to prevent the victim from escaping.
Type: mechanical
Trigger: location
Reset: manual
DC: 15 CR: 1
Effect: The jaws of the trap spring shut dealing 1d4 damage and halving movement (Dexterity save negates). If chained, the trap prevents movement from a fixed point unless a DC 22 locks or DC 26 strength check is made.
Price: 200 gp.
Enhancements: A version of this trap built for larger monsters can be purchased. It has a CR 2, price of 1,000 gp, DC 20, and deals 2d6+3 damage.
Box of Brown Mold
This trap is very simple. You put a brown mold in a box or chest and put it where someone can find it. When the box is opened, the mold's cold aura blasts all those in 5 feet. Short of finding some way to kill the mold without opening the box, there isn't an obvious way to disarm this trap.
Type: simple mechanical
Trigger: opening the box
Reset: automatic
DC: 20 CR: 2
Effect: The brown mold deals 3d6 cold damage to all within 5 feet who fail a DC 20 Con save.
Price: 3,000 gp.
Enhancements: none
Moving Executioner Statue
This trap is disguised as a statue that is conveniently holding a weapon of some sort. When triggered the statue swings the weapon, attacking the triggering creature before resetting.
Type: mechanical
Trigger: location
Reset: automatic
DC: 25 CR: 5
Effect: Attacks with two weapons, each at a +16 to hit (1d12+8), targeting two creatures.
When triggered, a large net sweeps multiple players upward trapping them.
Type: mechanical
Trigger: location
Reset: manual
DC: 16 CR: 1
Effect: Characters in a 10-foot square are grapple and suspended by the net. Dex save negates.
Price: 3,000 gp.
Enhancements: Improved Quality
Portcullis Trap
When triggered, a hidden portcullis falls damaging any underneath and blocking the passageway.
Type: mechanical
Trigger: location
Reset: manual
DC: 20 CR: 1
Effect: Portcullis falls blocking passageway. If someone is underneath it, they must make a Dexterity save or take 3d6 damage. The portcullis can only be lifted with a DC 25 strength check.
Price: 1,400 gp.
Enhancements: Bypass, Improved Quality
Razor-Wire across Hallway
When triggered, a razor-wire whips across the hallway cutting those in the way.
Type: mechanical
Trigger: location
Reset: none
DC: 22 CR: 1
Effect: Targets in two adjacent 5-foot squares must make a Dexterity save or take 2d6 slashing damage.
Price: 400 gp.
Enhancements: Bypass
Rolling Rock Trap
A large roll rolls down an incline toward the creature who triggers this trap.
Type: simple mechanical
Trigger: location
Reset: manual
DC: 20 CR: 1
Effect: The rock makes a +10 melee attack, dealing 2d6 bludgeoning damage).
Price: 1,400 gp.
Enhancements: Bypass
Swinging Block Trap
When this trap is triggered, a large block of some heavy material attacked to a chain swings down toward you.
Type: simple mechanical
Trigger: touch
Reset: manual
DC: 20 CR: 1
Effect: The swinging block makes a +5 melee attack dealing 4d6 points of bludgeoning damage.
