Black Ice

Slick ice covers the ground in a 10-foot square centered on a point within range and turns it into difficult terrain for the duration.

When the ice appears, each creature standing in its area must succeed on a Dexterity saving throw or fall prone. A creature that enters or attempts to stand in the area or ends its turn there must also succeed on a Dexterity saving throw or fall prone. The ice is nearly invisible and can only be seen with a successful Perception check. Creatures with heated body are not affected by Black Ice.