Baltron’s Black Sheen

You create a thin sheet of black ice that covers a 10-foot square centered on a point within range. Whenever a creature enters the area or ends its turn there, including when you first cast this spell, it must succeed on a Dexterity saving throw or fall prone.

At higher levels. When you cast this spell using a spell slot of 2nd level or higher, the size of the square increases by 5 feet for each slot level above 1st.