Rules Index | GM Screen

Designing a Trap

Source PRPG Core Rulebook pg. 423
Designing new traps is a simple process. Start by deciding what type of trap you want to create. Mechanical Traps: Simply select the elements you want the trap to have and add up the adjustments to the trap’s Challenge Rating that those elements require (see Table 13–3) to arrive at the trap’s final CR. From the CR you can derive the DC of the Craft (traps) checks a character must make to construct the trap (see page 424). Magic Traps: As with mechanical traps, decide what elements you want and then determine the CR of the resulting trap (see Table 13–4). If a player character wants to design and construct a magic trap, he, or an ally, must have the Craft Wondrous Item feat. In addition, he must be able to cast the spell or spells that the trap requires—or he must be able to hire an NPC to cast the spells for him.

Table 13-3: CR Modifiers for Mechanical Traps

Feature	CR Modifier
Perception DC
15 or lower	-1
16-20	—
21-25	+1
26-29	+2
30 or higher	+3
Disable Device DC
15 or lower	-1
16-20	—
21-25	+1
26-29	+2
30 or higher	+3
Reflex Save DC (Pit or Other Save-Dependent Trap
15 or lower	-1
16-20	—
21-25	+1
26-29	+2
30 or higher	+3
Attack Bonus (Melee or Ranged Attack Trap)
+0 or lower	-2
+1 to +5	-1
+6 to +10	—
+11 to +15	+1
+16 to +20	+2
Touch attack	+1
Damage/Effect
Average damage	+1 per 10 points of average damage
Miscellaneous Features
Alchemical device	Level of spell mimicked
Automatic reset	+1
Liquid	+5
Multiple targets (non-damage)	+1
Never miss	+2
Proximity or visual trigger	+1

Poison	CR of poison
Black adder venom	+1
Black lotus extract	+8
Bloodroot	+1
Blue whinnis	+1
Burnt othur fumes	+6
Deathblade	+5
Dragon bile	+6
Giant wasp poison	+3
Greenblood oil	+1
Insanity mist	+4
Large scorpion venom	+3
Malyass root paste	+3
Medium 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

Table 13-4: CR Modifiers for Magic Traps

Feature	CR Modifier
Highest-level spell effect	+Spell level
Damaging spell effect	+1 per 10 points of average damage

Challenge Rating of a Trap

Source PRPG Core Rulebook pg. 423
To calculate the Challenge Rating of a trap, add all the CR modifiers (see Table 13–3 or Table 13–4) to the base CR for the trap type.

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

Magic Trap: For a spell trap or magic device trap, the base CR is 1. The highest-level spell used modifies the CR (see Table 13–4).

Average Damage: If a trap (mechanical or magical) does hit point damage, calculate the average damage for a successful hit and round that value to the nearest multiple of 10. If the trap is designed to hit more than one target, multiply this value by 2. If the trap is designed to deal damage over a number of rounds, multiply this value by the number of rounds the trap will be active (or the average number of rounds, if the duration is variable). Use this value to adjust the Challenge Rating of the trap, as indicated on Table 13–3. Damage from poison does not count toward this value, but extra damage from pit spikes and multiple attacks does.

For a magic trap, only one modifier applies to the CR— either the level of the highest-level spell used in the trap, or the average damage figure, whichever is larger.

Multiple Traps: If a trap is really 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 by not falling victim to the first), characters earn XP for both traps by defeating the first one, regardless if the second one is also sprung.

Multiple Independent Traps: If two or more traps act independently (they do not depend on one another to activate), characters only earn XP for traps that they defeat.

Mechanical Trap Cost

Source PRPG Core Rulebook pg. 423
The cost of a mechanical trap is 1,000 gp × the trap’s Challenge Rating. If the trap uses spells in its trigger or reset, add those costs separately. If the trap cannot be reset, divide the cost in half. If the trap has an automatic reset, increase the cost by half (+50%). Particularly simple traps, such as pit traps, might have a greatly reduced cost, subject to GM discretion. Such traps might cost as little as 250 gp × the trap’s Challenge Rating.

After you’ve determined the cost by Challenge Rating, add the price of any alchemical items or poison you incorporated into the trap. If the trap uses one of these elements and has an automatic reset, multiply the poison or alchemical item cost by 20 to provide an adequate supply of doses.

Multiple Traps: If a trap is really two or more connected traps, determine the final cost of each separately, then add those values together. This holds for both multiple dependent and multiple independent traps.

Magic Device Trap Cost

Source PRPG Core Rulebook pg. 423
Building a magic device trap involves the expenditure of gp and requires the services of a spellcaster. Table 13–5 summarizes the cost information for magic device traps. If the trap uses more than one spell (for instance, a sound or visual trigger spell in addition to the main spell effect), the builder must pay for them all (except alarm, which is free unless it must be cast by an NPC).

The costs derived from Table 13–5 assume that the builder is casting the necessary spells himself (or perhaps some other PC is providing the spells for free). If an NPC spellcaster must be hired to cast them, those costs must be factored in as well (see Chapter 6).

A magic device trap takes 1 day to construct per 500 gp of its cost.

Table 13-5: Cost Modifiers for Magic Device Traps

Feature	Cost Modifier
Alarm spell used in trigger	—
One-Shot Trap
Each spell used	+50 gp × caster level × spell level
Material components	+ material component costs
Automatic Reset Trap
Each spell used	+500 gp × caster level × spell level
Material components	+material component costs × 100

Spell Trap Cost

Source PRPG Core Rulebook pg. 423
A spell trap has a cost only if the builder must hire an NPC spellcaster to cast it.

Craft DCs for Mechanical Traps

Source PRPG Core Rulebook pg. 423
Once you know the Challenge Rating of a trap, determine the Craft (traps) DC by referring to the values and modifiers given on Table 13–6.

Making the Checks: To determine how much progress a character makes on building a trap each week, that character makes a Craft (traps) check. See the Craft skill description for details on Craft checks and the circumstances that can affect them.

Table 13-6: Craft (Traps) DCs

Trap CR	Base Craft (Traps) DC
1-5	20
6-10	25
11-15	30
16+	35

Additional Components	Modifier to Craft (Traps) DC
Proximity trigger	+5
Automatic reset	+5

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