Pressure Pocket
Pent up gasses, hydrothermal vents in underground seas, the flow of subterranean waterways, and collapsing passageways in the endless tunnels of Underland can create pockets of immense pressure that bowl upward with immense force until reaching areas that contain them. Eventually these pressure pockets find release, their escape flinging superheated chunks of stone into the Howling Expanse to wreak havoc upon the tundra.
Forewarning. A nearby pressure pocket can be noticed with a Perception check to hear the soft clacking of rocks bouncing around the enclosed passage containing it. Failing to notice the pressure pocket and walking into the area of a tunnel adjoining it results in a Critical Failure.
Precarious Passageway. Any amount of weight pressed upon the area of the tunnel adjoining the containment passage (the walls, ceiling, or floor) causes the pressure pocket to explode inward resulting in a Failure
Once the pressure pocket has been noticed, an Engineering or Nature check can determine how much of the tunnel ahead must be traversed without touching the sides. Anyone with a fly speed but unable to hover must make an Acrobatics check to avoid dislodging anything with the air they displace, as does anyone that makes an Athletics check to jump a safe distance.
Critical Failure: The pressure pocket explodes inward with hurricane force dealing 36 (8d8) thunder damage. Each adventurer makes a Strength saving throw or is thrown 1d20 × 100 feet away from the pressure pocket taking 2 (1d4) bludgeoning damage for every 100 feet they are moved. In addition, the party suffers one level of fatigue and loses half of their Supply .
Failure: The pressure pocket explodes inward dealing 18 (4d8) thunder damage forcing the party to make Strength saving throws . On a failed save, an adventurer is thrown 1d10 × 100 feet away from the pressure pocket taking 2 (1d4) bludgeoning damage for every 100 feet they are moved, they suffer a level of fatigue , and they lose 2d4 Supply .
Success: The adventurers safely make it through the precarious passageway.
Critical Success: The adventurers adroitly make it through the precarious passageway and find something on the other side. Roll on the Boons and Discoveries table.