Grease Spell
D&D Grease Spell Description: A grease spell covers a solid surface with a layer of slippery grease. Any creature in the area when the spell is cast must make a successful Reflex save or fall. This save is repeated on your turn each round that the creature remains within the area. A creature can walk within or through the area of grease at half normal speed with a DC 10 Balance check. Failure means it can't move that round (and must then make a Reflex save or fall), while failure by 5 or more means it falls (see the Balance skill for details).
More: D&D Spells for Grease