Doom of the Slippery Rogue

A doom of the slippery rogue spell covers a 20-foot-by-20-foot section of wall or floor within range with a thin coating of grease. If a vertical surface is affected, each climber on that surface must make a successful DC 20 Strength (Athletics) check or immediately fall from the surface unless it is held in place by ropes or other climbing gear. A creature standing on an affected floor falls prone unless it makes a successful Dexterity saving throw. Creatures that try to climb or move through the affected area can move no faster than half speed (this is cumulative with the usual reduction for climbing), and any movement must be followed by a Strength saving throw (for climbing) or a Dexterity saving throw (for walking). On a failed save, the moving creature falls or falls prone.