Sylas's Water Lock

You conjure a sphere of magical water around an enemy's head in attempts to drown them. Choose one creature that you can see within range you cause it to take 2d8 Cold damage upon casting. The creature cannot speak and has disadvantage on attack rolls and Perception checks until the spell ends. The creature must succeed a constitution saving throw against your spell save Dc at the end of their following turns, on a successful save the effects of this spell ends. You can use a bonus action on each of your subsequent turns to cause this damage again as long as the target continues to be affected by the spell.

Using a Higher-Level Spell Slot. The damage increases by 1d8 for each spell slot level above 2.