At-Will TerrainMud Sink
A patch of innocuous mud conceals a clinging morass that proves hard to escape.
Check: Athletics check (moderate DC) to maneuver one creature adjacent to you and to the mud sink into a mud sink square.
Success: You slide the creature 1 square into the mud sink square adjacent to it. You then make the following attack against that creature.
Target: Melee 1; one creature
Attack: Level +3 vs. Reflex
Hit: The target is immobilized (save ends).
Aftereffect: The target is slowed (save ends).
Published in Dark Sun Creature Catalog, page(s) 136.