From Pathfinder Kingmaker, which isn't enabled.

Unstable Pit

HAZARD 0

Stealth +2

Description This open pit was once covered with branches- it's now visible, but its unstable edges are not obvious.

Crumbling Edge

Trigger A creature comes within 5 feet of the pit's edge

Effect The edge of the pit crumbles. The triggering creature must attempt a DC 19 Reflex save.

Critical Success The triggering creature steps back from the edge before it collapses.

Success The triggering creature falls Prone.

Failure The triggering creature falls prone and slides into the pit, taking 1d6 bludgeoning damage.

Critical Failure As failure, but 2d6 bludgeoning damage.

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