Traps are a classic element of adventure design, but in play are often abstracted away with a couple of skill checks (one to detect the trap, one to disarm it) or outmaneuvered by clever play.
Either way, the trap construction system presented in the Pathfinder Core Rulebook is more “mechanically sophisticated’ (i.e. complicated) than I think traps warrant, just to get a simple stat block. Given that traps are simple game elements, it would be appropriate that they have a simple creation system.
I think this can be done without too much effort.
Pathfinder Unchained provided a simplified monster creation system that can create reasonably balanced monsters much more easily than the system presented in the Bestiary. It might not be quite as adaptable as the default system and it might not be able to quite model all the monsters present in the books… but much of the time, it’s good enough.
Unchained Trap Baseline
First, set aside the trap construction rules from the Pathfinder Core Rulebook (which are basically the same as from the System Reference Document that started the whole Open Game Content thing, so don’t hold it against Pathfinder).
Pick the nature of your trap, and the intended Challenge Rating (CR). For instance, a trap might do damage, inflict a poison, or trigger a spell (though if the spell is primarily a damaging spell, use the damage guidelines instead if that gives a higher result). Many traps have an attack roll (such as a dart trap) or saving throw (fire trap); decide how that works. Traps also have a Perception check DC and a Disable Device check DC, but there’s no need to make a decision there yet — they all have it, you don’t have to pick how that works.
Look up the CR on the table below. This gives you the base effect (damage, poison grade, spell level), skill check DCs, and attack bonus or save DC. It also gives a certain number of points to use in customizing further.
|CR||Damage||Average||Poison Level||Spell Level||Attack||Save DC||Skill DC||Trap Points|
A basic arrow trap (CR 1) is a mechanical trap doing 1d8 points of damage (average 4 points), with an attack bonus of +1… and 3 points to further enhance the trap. For the sake of simplicity, let’s assume a 0-point trigger (I’ll explain later), increase the attack bonus to +11, and increase the Perception DC to 21 (this trap is tricky to find, but not too hard to disarm once you know it’s there).
Spell traps no longer have a base skill check DC of 25 + spell level. They have the same base skill check DC as other traps of their CR. Spend trap points to buy up the skill check DCs (1 point per 5-point increase to one skill check DC) and remember that a character must have the trapfinding ability to disarm a spell trap using Disable Device.
There are many modifiers possible.
These modifiers adjust the baseline values. More than one point can be spent on a single modifier.
- Increase Effect: Each point spent increases the effect of the trap by ‘one CR’. This does not increase the attack bonus, save DC, or skill DCs.
- Additional Effect: Each point spent allows adding 1 CR from another effect (such as adding basic damage to a spell trap, or adding poison to a damage trap. This does not increase the attack bonus, save DC, or skill DCs.
- Increase Attack Bonus: Each point spent adds 5 to the attack bonus by +5.
- Increase Save DC: Each point spent adds 3 to the save DC.
- Increase Perception DC: Each point spent adds 5 to the DC of Perception checks to find the trap.
- Increase Disable Device DC: Each point spent adds 5 to the DC of Disable Device checks to disable the trap.
Increase Effect and Additional Effect each cost 1 point per CR improved. That is, adding a level 1 spell to a trap will cost 3 trap points, adding 2d8 points of damage to trap will cost 2 trap points.
Increase Attack Bonus, Increase Save DC, Increase Perception DC, and Increase Disable Device DC each use the baseline value 4 CR higher (so +5 to attack bonus or skill check DC, +3 to saving throw DC). Armor class and skill ranks both can increase faster than level, saving throw bonuses tend to advance slower.
These modifiers change how the trap works, or elements other than the baseline.
- Alchemical Device: Spend points as if adding an Additional Effect, above.
- Automatic Reset: Spend 1 point to cause the trap to automatically reset.
- Liquid: Spend 5 points if the trap involves a danger of drowning if the victims cannot escape.
- Multiple Targets: Spend 2 points for each anticipated doubling of the number of potential targets (typically by area of effect — a trap that targets immediately in front of a door would not have this modifier, a trap that targets the area in a 10-foot radius around a door might be expected to hit about 4 targets, and cost 4 trap points).
- Never Miss: Spend 2 points and the trap neither attacks nor allows a saving throw once triggered, but must now have an onset delay. The trap cannot Sell Back (see below) attack bonus or save DC.
- Touch Attack: Spend 1 point to cause the trap to target touch AC (ranged or melee) instead of full AC.
- Trigger: Spend 1 point to give the trap a proximity or visual trigger.
I changed how Multiple Targets works here because doubling the CR for multiple targets seemed too expensive (and poorly followed in the source material). Normally doubling the number of opponents in an encounter increases the CR by 2 rather than doubling it, so I applied similar reasoning here.
I suspect that in the end I’ll replace ‘multiple targets’ with ‘area of effect’ costs.
Just as trap points can be spent to increase baseline values, baseline values can be sold back to get additional trap points.
- Reduce Damage: Gain 1 point for each 1d8 points damage is reduced.
- Reduce Poison: Gain 1 point for each CR the poison is reduced.
- Reduce Spell: Gain 1 point for each CR the spell is reduced.
- Reduce Attack Bonus: Gain 1 point per 5 points the attack bonus is reduced. This cannot be done if the trap is Never Miss, above.
- Reduce Save DC: Gain 1 point per 3 points the save DC is reduced. This cannot be done if the trap is Never Miss, above.
- Reduce Perception DC: Gain 1 point per 5 points the Perception check DC is reduced.
- Reduce Disable Device DC: Gain 1 point per 5 points the Disable Device check DC is reduced.
At first look, it seems poison and spell effects can sometimes be sold back without reducing effect. This is true, but increasing the CR from odd to even does increase attack bonus, save DC, and skill DCs, it neither gives additional effect nor additional trap points. As such, I accept that these can be a ‘free’ trap point.
Sample CR 1 Traps
A few sample traps to test this out.
Missile Trap (CR 1)
This is a basic CR 1 damaging trap. Baseline is 1d8 damage, +1 attack bonus, DC 16 skill checks, and 3 trap points.
Effect Attack +6 ranged (1d8/x3); Trigger touch; Reset manual; Perception 21; Disable Device 21
This is a little weaker (attack bonus is +6 rather than +15) but slightly harder to find than the same trap from the Pathfinder Core Rulebook. For the same CR it could be made more accurate (+11 or +16) at the cost of keeping one or both skills at DC 16.
Alternatively, the trap could have the lower Perception and Disable Device, but launch a more accurate (+11) and damaging (2d8/x3) missile.
Effect Attack +11 ranged (2d8/x3); Trigger touch; Reset manual; Perception 16; Disable Device 16
Quite a bit easier to see, stands a good chance of hitting what triggered it, but relatively easy to find and disarm.
Pit Trap (CR 1)
A classic. Another damaging trap, but this one using a saving throw. Baseline is d8 damage, save DC 12, skill DC 16.
Effect 1d8 fall, Reflex DC 18 avoids; Trigger location; Reset manual; Perception 21; Disable Device 16
Normally falls do 1d6 points per 10 feet, Traps Unchained works with units of damage of 1d8… I call this close enough. Two improvements to the Reflex save DC and one to Perception (it’s hard to find). Again, this is somewhat weaker than the one from the Pathfinder Core Rulebook, but this is probably more in line with a CR 1 trap.
Effect 3d8 ‘fall and spikes’, Reflex DC 15 avoids; Trigger location; Reset manual; Perception 16; Disable Device 16
A simplified ‘spiked pit’: fall 10 feet onto spikes, Reflex save to avoid. Rather than treating the spikes as a separate trap, it’s just part of the damage taken when falling to this one. Trap points were spent to increase the damage (potentially enough to kill a level 1 PC) but the skill check DCs aren’t too difficult. This is a threat mostly to the unobservant and unfortunate.
Poison Dart Trap (CR 1)
Another classic, darts with something nasty on them. This is primarily a damage trap with level 1 poison (greenblood oil) applied.
Greenblood Poison Dart
Effect Attack +1 ranged (1d8 plus greenblood oil); Trigger touch; Reset manual; Perception 16; Disable Device 16
All trap points were spent on the poison, leaving the base damage, attack bonus, and skill check DCs unimproved.
Greenblood oil is a pretty vicious thing to hit a level 1 party with, but with only the baseline skill checks to discover and disable the trap, and only a +1 attack bonus this seems unlikely to matter.
Greenblood Poison Needle
Effect 1 point plus greenblood oil, Reflex DC 12 avoids; Trigger touch; Reset manual; Perception 21; Disable Device 16
This is a needle such as might be found in the lock of a treasure chest. This trap uses a Reflex save instead of an attack roll, spends the trap points on the poison, and sells back the base damage (to a minimum of 1 point — even a single point of DR would prevent the poison from working) to increase the Perception check needed to find the trap.
Sample CR 6 Traps
Let’s jump up a bit, look at some more dangerous traps.
Flame Strike Trap
This is a magic trap, and will need some careful comparison to the core version.
Core Flame Strike Trap
Effect Spell effect (flame strike, 8d6 fire damage, Reflex save 17 halves); multiple targets (10-foot radius); Trigger proximity; Reset none; Perception 30; Disable Device 30 (trapfinding needed)
Get too close, go fwoomf! Simple enough. Let’s look at the unchained version.
Unchained Flame Strike Trap
Effect 6d8 fire damage, Reflex save 16 halves; multiple targets (10-foot radius); Trigger proximity; Reset none; Perception 22; Disable Device 22 (trapfinding needed)
The primary effect here is damage rather than spell effect, so I wrote it up as a damage trap. 8d6 and 6d8 are more or less the same, so I started with a CR 6 damage trap. This gave a baseline 6d8 damage, save DC 16, skill DCs 22, and 4 trap points.
I put all 4 points on multiple targets. In many situations this trap might be expected to catch only 1 or 2 targets, but I expect this would be placed such that ‘everyone’ would be there. No changes to the save DC (which was close to core value) or the skill check DCs.
I could reduce the effect by 1 CR (5d8 damage) to increase one of the other values (save DC or Perception DC, most likely).
Wyvern Arrow Trap
A much more dangerous trap than the greenblood oil dart, I would make this a CR 11 trap (baseline CR for a level 5 poison). This allows a level 5 poison, +13 attack bonus, skill DC 28, and 5 trap points.
Wyvern Arrow Trap (CR 11!)
Effect Attack +13 (wyvern poison/x3); Trigger location; Reset none; Perception 28; Disable Device 28
The same trap in the Pathfinder Core Rulebook actually isn’t as good as this. The attack bonus is about the same (+15 rather than +13 as shown here) and it does 1d6 base damage, but the skill DCs are both 6 points higher than the core DC 22. I could sell back both skills one grade and buy the difference in damage, leaving me with 6 trap points. It’s evident that CR 11 is too high, it might be better to CR 8 and buy back up.
Wyvern Arrow Trap (CR 8)
Effect Attack +10 (1d8 + wyvern poison/x3); Trigger location; Reset none; Perception 25; Disable Device 25
As a CR 8 poison trap, there are 4 trap points. Three go to increasing the CR of the poison from 3(.5) to 5, 1 goes to adding 1d8 damage. It would be nice to get the damage bonus up a bit more.
I would be willing, if I felt it necessary to align with the core version of the trap, to sell back ‘half’ of each of the skill check DCs to get another trap point, to push the attack bonus up to +15. For simplicity I’d probably sell back one of the skill checks (likely Disable Device).
Wyvern Arrow Trap (CR 9)
Effect Attack +16 (1d8 + wyvern poison/x3); Trigger location; Reset none; Perception 26; Disable Device 26
At CR 9, there are more resources available. The baseline attack +11 got bumped by 1 grade to +16, only 2 trap points were needed to get to wyvern venom, leaving 2 points unassigned (and both skill DCs 4 points higher than core).
For modeling the CR 6 wyvern arrow trap, CR 8 looks like the best match overall.
For a first cut, I’m pretty happy with this. The system is still pretty flexible, while being (I think) simpler to apply than the regular trap construction rules. I suspect I’ll want to revisit how the poison levels work… maybe instead of setting them higher it might be better to put a surcharge on Additional Effect modifiers, or maybe just for poison.
I’m almost certainly going to replace ‘multiple targets’ with ‘area of effect’, though.