4E lends itself to improvised game play yet this seems a curious omission for a system that does. So what's missing? The ability to throw together traps using only the Difficulty Class and Damage By Level table, a few keywords and knowing how many xp make a successful quick & dirty skill challenge with Acrobatics, Athletics, Arcana, Dungeoneering, Perception and Thievery?
Come to think of it, it does sounds a bit 'preparation needed'. Anyway - three trap related things. Feel free to bend, fold, spindle and mutilate. And if you want to, modify them as well.
The See-Saw Floor (Level 1 Obstacle 100xp)
Trap: A 20' high triangular pivot is set at 20' along a 40' long and 20' deep pit. The pit is as wide as the corridor. Apart from the initial impact, the corridor ahead is blocked off until the floor is brought back in line with the rest of the corridor.
Perception: DC15 to notice the stonework on the floor appears a bit worn along one side and is made of a neat section of flooring material.
Trigger: Trap activates when the first five feet at either end of the see-saw has more than 10lbs weight placed on it.
Attack: Immediate Reaction. +3 vs. Reflex.
Hit: Take 2d10 falling damage and fall prone. Corridor is blocked 20' ahead by the other end of the see-saw going up.
Miss: Target ends their move action and takes no damage.
Effect: See-saw trap is revealed.
- A successful Athletics check (DC10/20 from standing) will let the character jump to the half-way point. From that point, they can make an Athletics check (DC20, no running) to clear the remaining distance.
- A successful Athletics check (DC15) lets a character climb out.
- An adjacent character can with a Thievery check (DC20) disable the see-saw by forcing a piton or spike into the corner between the floor and the edge of the see-saw. One person can cross per object forced in.
Stone Block Trap (Level 7 Lurker, 300xp)
Trap: A pressure plate on the floor triggers the fall of a large stone block from above onto the area of the pressure plate. The stone block is heavy and may trap a victim under it. Once the block has been there for 10 minutes, the steel chain on top of it begins to winch it back up.
Perception: DC 24 to spot the flagstone with the pressure plate (which seems a little pushed in in comparison with the other flagstones).
Trigger: Standing on the pressure plate (which is the size of a square) pushes the block out of place and onto the victim.
Attack: Immediate. +8 vs. Reflex.
Hit: Take 2d8+5 damage and make a successful Strength check (DC19) or stop moving. Each round under the block inflicts 1d6 ongoing damage unless the strength check is made. Adjacent characters may aid the victim and get a +2 bonus by using the chain in the top of the rock..
Miss: No damage.
Event: Square with stone block and chain is considered difficult terrain until the winch at the top of the chain activates after 10 minutes and pulls the block back up (this takes a minute).
- Once the block has fallen, adjacent characters may use the chain to lift the block off the plate and cause the trap to reset. This requires a Strength check (DC17). The pressure plate can then be avoided by an Athletics check (DC5/10 from standing start).
- An adjacent character with a successful Thievery check (DC28) disable the pressure plate.
Moren Calidarn was one of the luminaries among the trapsmiths of his generation (long dead now save for a handful of liches and other ne'er-do-wells) and his book is used as a primer for those who craft (and who attempt to bypass) such devices. Written in the manner of a sage's bestiary, it uses flowery language and metaphor to describe gruesome devices encountered in a dungeon or other setting.
Once a trap has been spotted with a successful Perception check, if consulted (which takes 1d6 minutes) it will give a +2 bonus to Thievery checks attempting to disable the trap. Attempting to construct one of the traps described in the Bestiary requires an Insight roll (DC20) to get past the flowery language. Costs and materials for the traps should be expensive and at DM fiat.
The book is worth 250gp to the right buyer. Certain bands of rogues may have an interest in specific copies which have been annotated by former associates.