I recently noticed that arrow traps got tougher in PFRPG. In D&D 3.0 and 3.5, a CR 1 arrow trap attacked with a bonus of +10 and did 1d6 damage. In PFRPG, a CR 1 arrow trap attacks at +15 and does 1d8+1 damage. Does anyone know why Paizo made this change?
I'm looking now at a 3.0 module with a CR 1/2 arrow trap, which attacks at +5 and does 1d6 damage. Another arrow trap has a CR of 1/3, an attack bonus of +2, and does 1d6. If I were to run this in PFRPG, I feel safe in assuming that those traps should do 1d8+1 damage, but what about attack bonus? Should I just add 5?
I would recommend just using it "as is". Pathfinder is intended to be backward-compatible with 3.x material, and the details are small enough that it might not be worth worrying about.
Pathfinder example traps start with a CR of 1. You can modify that to a CR of 1/2 by reducing the +15 attack to a +10.
Perception and Disable DCs are also a factor, as is the average damage... but for a single attack trap, damage of 1d6 (avg 3.5) and 1d8+1 (avg 5.5) aren't different enough to change the CR.
If it really bothers you, you could use the trap-building rules to determine what the CR should be in Pathfinder, and adjust XP awards appropriately. Some of the quotes statistics seem like CR 1/3 or 1/4 in Pathfinder, which is getting really low depending upon the adventure level.
Alternatively, you could use the CR as a guide and re-build the traps, modifying Perception, Disable Device, Attack, and Damage until it fits the CR.
A blanket plan of 1d8+1 damage and adding +5 to the attack is probably "close enough" in most cases.
Thanks. I see that an attack bonus anywhere from +1 to +5 would lower the CR by 1 (that is, from 1 to 1/2). So if I want the minimum danger to my party for the CR of 1/2, I might as well give both traps an attack of +1 and both with a CR of 1/2. :)