Aftershock

If an enemy hits you with a melee attack or melee spell attack, you can use this reaction to send 3d10 force damage back at the attacker. The enemy must make a dexterity save. If the enemy fails the take the full damage from aftershock. If they are successful, they take half damage. 

At Higher Level(s). Damage from initial reaction go up to 4d10 in a 3rd spell slot, and 5d10 in a 4th spell slot, and 6d10 in a 5th spell slot.