Poisoned Tempest

From Xanathar's Guide to Everything, page 118.

Complex trap (level 11-16, deadly threat)

This fiendish trap was built to eliminate intruders who infiltrate a yuan-ti temple. The trap is a room, 60 feet on a side, with 5-foot-wide stone doors in the middle of each wall. In each corner of the room stands a 10-foot-tall statue of a great serpent, coiled and ready to strike. The eyes in each statue are rubies worth 200 gp apiece.


 * Trigger: This trap activates when a ruby is pried from one of the statues. Each statue's mouth slides open, revealing a 1-foot-wide pipe that runs down its throat.
 * Initiative: The trap acts on initiative count 20 and initiative count 10.
 * Active Elements: The trap fills the room with poison and other deadly effects.
 * Locked Doors (Initiative 20): The four doors to this room slam shut and are locked in place by magic. This effect activates only once, the first time the trap is triggered.
 * Poison Gas (Initiative 20): Poison gas floods the room. Each creature inside must make a DC 20 Constitution saving throw, taking 33 (6d10) poison damage on a failed save, or half as much damage on a successful one.
 * Tempest (Initiative 10): Air and gas boils from the trap. Roll a d6, and consult the following table.
 * Dynamic Elements: The longer the poison gas remains in the room, the more lethal it becomes.
 * Increased Potency: The damage from the Poison Gas element increases by 11 (2d10) each round after it activates, to a maximum of 55 (10d10).
 * Countermeasures: There are a few ways that the trap can be overcome.
 * Open the Doors: Opening the doors is the quickest way to circumvent the trap, but they are warded with magic. To open the doors, a character must first succeed on a DC 20 Wisdom (Perception) check to find the locking mechanism. A successful DC 20 Intelligence (Arcana) check is then required to disable the sphere of force that surrounds the lock (Dispel Magic is ineffective against it). Success on a DC 20 Dexterity check using thieves' tools picks the lock. Finally, a successful DC 20 Strength (Athletics) check is needed to push the door open. Each check requires an action.
 * Disable the Statues: A statue can be disabled by blocking the flow of gas from its mouth. Heavily damaging a statue is a bad idea, for doing so leaves the gas vents open. Reducing a statue to 0 hit points (AC 17; 20 hp; resistance to fire, piercing, and slashing damage; immune to poison and psychic damage) or making a successful DC 20 Strength check to break it cracks the statue and increases the Poison Gas damage by 5 (1d10). A successful DC 20 Dexterity check using thieves' tools, or a successful DC 15 Strength check made to block up the statue with a cloak or similar object, decreases the poison damage by 5 (1d10). Once a character succeeds on the check, someone must remain next to the statue to keep it blocked up. When all four statues are blocked in this manner, the trap deactivates.