The substance of the Elemental Chaos sometimes exhibits a destructive will, especially in the form of elementals, but sentience is not necessary for the semblance of living behavior. A prime example is crawling earth, which resembles normal ground but animates when stepped on, then quiets after a few moments.
Effect: When any creature ends its movement in a square of crawling earth, it triggers that square and any contiguous squares containing that terrain. The ground rises up and moves 1d4 squares in a random direction, carrying along any creature in that space. The movement is so quick and jarring that a creature in a square of crawling earth must make a saving throw to avoid being knocked prone.
A section of crawling earth is usually no larger than 4 squares on a side, but wider areas exist in particularly unstable sections of the Elemental Chaos.
Usage: The Elemental Chaos contains several fantastic terrain types that create a dynamic environment, but crawling earth does the best job. Such terrain discourages creatures from ending their movement in certain spaces, forcing them to move farther than they otherwise would (which favors melee combatants) or discouraging movement altogether (making them easy prey for ranged attacks). You might also set the crawling earth’s movement in a specific direction or toward a given point to push the action a certain way or to enhance monsters’ control effects.
Published in The Plane Below, page(s) 13.