Cries of the Damned

You speak a creature's true name, calling forth to it its innermost demons to assail the creature. It takes 6d6 psychic damage at the start of its next turn, the next round it must make a constitution or wisdom saving throw (its choice) or take the full damage again. On a successful save the damage dice are reduced by a d6. This process continues until the damage reaches zero d6s, or the creature takes 70 or more psychic damage.