Astor's Oil Slick

Slick oil covers the ground in a 20-foot square centered on a point within range and turns it into Difficult Terrain for the duration.

When the oil appears, each creature standing in its area must succeed on a Dexterity saving throw or fall prone. Each creature that enters the area for the first time on a turn or ends its turn there must also succeed on a Dexterity saving throw or fall prone.

The oil is flammable. Any 5-foot square of oil exposed to fire burns away in 1 round, dealing 2d4 Fire damage to any creature that starts its turn in the fire.