Blood Siphon

You siphon the blood from a nearby creature to bolster your own defences. Choose a creature that you can see within range. That creature must make a Constitution saving throw, taking 1d8 necrotic damage on a failure and half that on a success. You then gain temporary hit points equal to half the necrotic damage dealt. These temporary hit points last until the end of your next turn. This spell has no effect on undead or constructs. 

At Higher Levels. When you cast this spell with a spell slot of 2nd level or higher, the damage increases by 1d8 for each level above 1st.