Black Ice

Slick black ice covers the ground in a 5-foot radius 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 the area or ends its turn there must also succeed on a Dexterity saving throw or fall prone

For every level above 1, the radius of the affected area increases by 5 feet.