Black Ice

The ground in a 15-foot square within range becomes icy and is difficult terrain. If the area of effect intersects with a wall or ceiling the effect will continue onto that surface. This change lasts for 1 minute.

When the ice appears, each creature standing in its area must succeed on a Dexterity saving throw or fall prone. A creature that enters the area or ends its turn there must also succeed on a Dexterity saving throw or fall prone.