In our game, an enemy cast Grease in a 10x10 area. But two of those squares in that area are stairs that lead down and are therefore below the level of the floor where the Grease was cast. What happens in those two squares? Does the grease hover in mid-air, or fall down onto the stairs, or not happen because there's no "surface" there? Surprisingly I can't find any ruling on this!
Thanks!
