Life Siphon (UA)

You fire an orb of psionic energy fueled by your life force at a creature you can see within range. Make a ranged spell attack against the target. On a hit, the target takes 1d10 Psychic damage and you can expend one Hit Point Die to increase the damage by 1d10.

Using a Higher-Level Spell Slot: The damage increases by 1d10 and the number of Hit Dice you can expend increases by one for each spell slot level above 1.