Step 3: Figure out the Numbers

Now that you have figured out the trigger, reset, and bypass elements, it’s time to define the trap itself. You need DCs for Search and Disable Device, plus attack/ saving throw and damage/effect information. Keep your list of cost and CR adjustments running; many of these elements also change those factors.

Search and Disable Device DCs

The builder sets the Search and Disable Device DCs for a mechanical trap. For a magic trap, the values depend on the highest-level spell used.

Mechanical Trap: The base DC for both Search and Disable Device checks is 20. Raising or lowering either of these affects the base cost and CR as shown on Table 2–2.

Magic Trap: The DC for both Search and Disable Device checks is equal to 25 + spell level of the highest-level spell used. Only characters with the traps ability can attempt either check. These values do not affect the trap’s cost or CR.

Other Ways to Beat a Trap

It’s possible to ruin many traps without using Disable Device, of course. Some possibilities are listed below.

Ranged Attack Traps: Once you know the trap is there, the obvious way to disable it is to smash the mechanism—assuming you have access to it. Failing that, you can plug up the holes from which the missiles emerge. This option not only gives you total cover relative to the trap, but it also prevents the trap from firing unless its ammunition does enough damage to break through the plugs. This option also works for magic traps with effects that have obvious emergence points.

Melee Attack Traps: You can disable these devices by smashing the mechanism or blocking the weapons, as noted above. Alternatively, if you study the trap as it triggers, you might be able to time your dodges just right to avoid damage. If you are doing nothing but studying the trap when it first goes off, you gain a +4 dodge bonus against its attacks if you trigger it again within the next minute. (After that, you forget the exact timing and arc of the attack, so no bonus applies.)

Pits: Disabling a pit trap generally ruins only the trap door, making it an uncovered pit. Options such as filling in the pit or building a makeshift bridge across it are applications of manual labor, not Disable Device. You could also disable any spikes at the bottom of the pit by attacking them—they break just like daggers do.

Magic Traps: Dispel magic works wonders here. If you succeed at a caster level check against the creator’s level, you suppress the trap for 1d4 rounds. This works only with a targeted dispel magic, not the area version.

Attacks/Saving Throws

A trap usually either makes an attack roll or forces a saving throw to avoid it. Consult one or more of following sections to determine which option is appropriate for your trap, based on its type. Occasionally, a trap uses both of these options, or neither (see Never-Miss, page 29).

Pits: These are holes (covered or not) that characters can fall into and take damage. A pit needs no attack roll, but a successful Reflex save (DC set by the builder) avoids it. Other save-dependent mechanical traps also fall into this category.

Ranged Attack Traps: These traps fling darts, arrows, spears, or the like at whoever activated the trap. The builder sets the attack bonus.

Melee Attack Traps: These traps include sharp blades that emerge from walls and stone blocks that fall from ceilings. Once again, the builder sets the attack bonus.

Damage/Effect

The effect of a trap is simply 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.

If your trap does hit point damage, calculate the average damage for a successful hit and round that value to the nearest multiple of 7. (Damage from poisons and pit spikes does not count toward this value, but mighty damage and extra damage from multiple attacks does. For example, if a trap fires 1d4 darts at each target, the average damage is the average number of darts × the average damage per dart, rounded to the nearest multiple of 7, or 2.5 darts ×2.5 points of damage = 6.25 points, which rounds to 7.) Consult Table 2–2 to determine the CR bonus.

Pits: Falling into a pit deals 1d6 points of damage per 10 feet of depth.

Ranged Attack Traps: These traps deal whatever damage their ammunition normally would. A trap that fires longbow arrows, for example, deals 1d8 points of damage per hit. You can also build mighty traps that deal extra damage. For example, a mighty (+4 Str bonus) ranged attack trap that fires shortspears could deal up to 1d8+4 points of damage per successful hit.

Melee Attack Traps: These traps deal the same damage as the melee weapons they “wield.” In the case of a falling stone block, you can assign any bludgeoning damage you like, but remember that whoever resets the trap has to lift that stone back into place. You can also build mighty traps that deal extra damage.

Spell Traps: Spell traps produce the spell’s effect as described in the appropriate entry in the Player’s Handbook. as with all spells, each spell-based trap that allows a saving throw has a save DC equal to 10 + spell level + caster’s relevant ability modifier.

Magic Device Traps: These traps produce the effects of any spells included, as described in the appropriate entries in the Player’s Handbook. If the spell in a magic device trap allows a saving throw at all, its save DC equals 10 + spell level ×1.5. Some spells make attack rolls instead.

Special: Some traps have miscellaneous features that produce special effects, such as drowning for a water trap or ability damage for poison. Saving throws and damage depend on the poison (see Table 2–1) or are set by the builder, as appropriate.

Miscellaneous Trap Features

Some traps include optional features that can make them considerably more deadly. The most common such features are listed below.

Alchemical Device: Mechanical traps may incorporate alchemical devices or other special substances or items, such as tanglefoot bags, alchemist’s fire, thunderstones, and the like. Some such items mimic spell effects. For example, the effect of a tanglefoot bag is similar to that of an entangle spell, and the effect of a thunderstone is similar to that of a deafness spell. If the item mimics a spell effect, it increases the CR as shown on Table 2–2.

Gas: With a gas trap, the danger is in the inhaled poison it delivers. Traps employing gas usually have the never-miss and onset delay features.

Never-Miss: When the entire dungeon wall moves to crush you, your quick reflexes won’t help, since the wall can’t possibly miss. A trap with this feature has neither an attack bonus nor a saving throw to avoid, but it does have an onset delay (see below). Most water and gas traps are also never-miss.

Multiple-Target: Traps with this feature can affect more than one character.

Onset Delay: An onset delay is the amount of time between when the trap is sprung and when it inflicts damage. A never-miss trap always has an onset delay.

Poison: Traps that employ poison are deadlier than their nonpoisonous counterparts, so they have correspondingly higher CRs. To determine the CR modifier for a given poison, consult Table 2–4, above. Only injury, contact, and inhaled poisons are suitable for traps; ingested types are not.

Some traps (such as a table covered with contact poison) simply deal the poison’s damage. Others, such as poisoned arrows, deliver ranged or melee attacks as well.

Table 2–18: CR Modifiers by Poison Type

Poison Type	CR Modifier
Black adder venom	+1
Black lotus extract	+8
Bloodroot	+1
Blue whinnis	+1
Burnt othur fumes	+6
Carrion crawler brain juice	+1
Deathblade	+5
Dragon bile	+6
Giant wasp poison	+3
Greenblood oil	+1
Insanity mist	+4
Large scorpion venom	+3
Malyss root paste	+3
Medium-size spider venom	+2
Nitharit	+4
Purple worm poison	+4
Sassone leaf residue	+3
Shadow essence	+3
Small centipede poison	+1
Terinav root	+5
Ungol dust	+3
Wyvern poison	+5

Pit Spikes: Treat spikes at the bottom of a pit as daggers, each with a +10 attack bonus. The damage bonus for each spike is +1 per 10 feet of pit depth (to a maximum of +5). 1d4 spikes attack each character who falls into the pit. Pit spikes do not add to the average damage of the trap (see above), nor do their damage bonuses constitute mighty damage.

Pit Bottom: If there’s something other than spikes at the bottom of a pit, it’s best to treat that as a separate trap (see multiple traps, below) with a location trigger that activates on any significant impact, such as a falling character. Possibilities for pit bottom traps include acid, monsters, or water (which reduces the falling damage; see the Obstacles, Hazards, and Traps section in Chapter 4 of the DUNGEON MASTER’s Guide).

Touch Attack: This feature applies to any trap that needs only a successful touch attack (melee or ranged) to hit.

Water: Any trap that involves a danger of drowning (such as a locked room filling with water or a patch of quicksand that characters can fall into) is in this category. Traps employing water usually have the never-miss and onset delay features (see above).

CR for the Trap

To calculate the CR for a trap, add all the CR modifiers collected above to the base CR value for the trap type.

Mechanical Trap: The base CR for a mechanical trap is 0. If your final CR is 0 or below, add features until you get a CR of 1 or better.

Magic Trap: For a spell or magic device trap, the base CR is 1. Only the highest-level spell used modifies the CR.

Multiple Traps: If a trap is two or more connected traps that affect approximately the same area, determine the CR of each one separately.

Multiple Dependent Traps: If one trap depends on the success of the other (that is, you can avoid the second trap altogether by not falling victim to the first), they must be treated as two separate traps.

Multiple Independent Traps: If two or more traps act independently (that is, neither depends on the success of the other to activate), use their CRs to determine their combined Encounter Level as though they were monsters, according to Table 4–1 in the DUNGEON MASTER’s Guide. The resulting Encounter Level is the CR for the combined traps.