Erul's Moondance

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 the target's space becomes bathed in a 5-foot cylinder of moonlight until the start of your next turn. The next attack against a creature within the spell's area has advantage and does extra cold damage equal to your spellcasting ability modifier on a hit. 

The spell's damage increases when you reach certain levels. At 5th level, the melee attack deals and extra 1d8 cold damage to the target on a hit, and the secondary damage deals an extra 1d8 cold damage + your spellcasting ability modifier. Both damage rolls increase by 1d8 at 11th level (2d8 and 2d8) and 17th level (3d8 and 3d8).