Deep Collapsing Dungeon

Cracks criss-cross the ceiling. With each motion and loud noise, tremors shake the floor.

When a creature disturbs or destroys a focal point central to the dungeon (such as a pillar, a sacred object, or a magic rune), the dungeon begins to collapse. Once the collapse begins, it can’t be undone. Creatures in the dungeon must escape before the dungeon is completely destroyed.

Exploration. An Engineering check or an examination of the dungeon’s focal point reveals that the dungeon’s structure is unstable, and that it could be shored up with support beams. An examination of the ceiling or floor reveals cracks along the ceiling, as well as dust and dirt that sifts down to the floor. When a creature touches the dungeon’s focal point, creatures within 30 feet of it feel a faint tremor.

Collapse. Roll initiative. On initiative count 20, a 40 by 40-foot unstable area appears centered on the focal point. Each successive turn on initiative count 20, the size of the unstable area increases by 20 feet in all directions.

A creature that starts its turn inside the unstable area makes a Dexterity saving throw . On a failure or success, the creature triggers this challenge’s Failure or Success effect. A roll of 1 triggers a Critical Failure.

Once the unstable area completely encompasses the dungeon, the dungeon’s ceiling collapses, burying all creatures and objects in rubble. Each creature in the dungeon suffers a Critical Failure, and the effect ends. If the dungeon is composed of multiple levels, a collapse occurs once the unstable area encompasses a level but affects only that level until the unstable area spreads further.

Once the collapse begins, a Large object (such as a statue or a wall of stone) propped against the ceiling in the unstable area prevents the area from growing for 1 round.