Abyssal Siphon

You create a beam of necrotic energy between you and a target creature. Make a ranged spell attack against it. If hit, the target takes 2d6 necrotic damage and you regain hit points equal to half the damage dealt. 

Until the end of your next turn consecutive casting of this spell gains advantage on its attack roll. Any other spell cast between this and the next breaks the beam and ends this affect.

This spell's damage increases by 1d6 when you reach 5th level (3d6), 11th level (4d6), and 17th level (5d6).