Drain Undead

You point your finger at any undead creature within 15 feet. The creature must roll a constitution saving throw or take 2d6 damage, and you regain hit points equal to half the amount of damage dealt.

When used on a willing creature, this spell deals maximum damage, and you regain hit points equal to the amount of damage dealt. 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d6 for each slot level above 1st.