PHB

Phantasmal Killer

4-level Illusion

You tap into the nightmares of a creature you can see within range and create an illusory manifestation of its deepest fears, visible only to that creature. The target must make a Wisdom saving throw. On a failed save, the target becomes frightened for the duration. At the end of each of the target's turns before the spell ends, the target must succeed on a Wisdom saving throw or take 4d10 psychic damage. On a successful save, the spell ends.
At higher levels: When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d10 for each slot level above 4th.