Blood Siphon

You point at a target with the tip of your finger and attempt to siphon their life force to strengthen your own. Make a melee spell attack against a target with a successful  attack dealing 1d4 necrotic damage and you gain half the damage delt as temporary hit points. 

The spell's damage increases by 1d4  when you reach 5th level (2d4), 11th level (3d4),  and 17th level( 4d4).