Cold Mist Blade

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 you cause a blue mist to cling to the target.  If the creature uses a Bonus Action before you next turn, takes Cold Damage equal to your spell casting modifier.

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