Erratic Rebuke

In response to taking damage from a creature
within 60 feet that you can see, you point your
finger, and the creature that damaged you is
momentarily surrounded by an elemental energy.
The creature must make a Dexterity saving throw.
It takes 2d10 damage of a type randomly chosen
between fire, lightning, and cold on a failed save,
or half as much damage on a successful one.
You regain the ability to use this feature after a
long rest.