Blood Tap

You point at a creature within range and send razors of invisible energy towards them. The target must succeed on constitution saving throw or take 1d4 slashing damage and, if the creature is not a construct or undead, it suffers an addition 1d8 necrotic damage at the start of its turn as it begins to bleed out. 

This spell’s necrotic damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).