Black Butterfly

You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and a shimmering swarm of ethereal starry butterflies spiral around the target. Until the end of your next turn, the target sheds bright light in a 5 foot radius and dim light for an additional 5 feet. The target has disadvantage on the next saving throw it makes against a spell before this spell ends. Additionally, whenever the target makes a Constitution saving throw to maintain Concentration before the spell ends, it must subtract 1d4 from that roll and takes 1d4+1 Psychic damage if it fails that save.