Talons of Icharus

The creature you touch must make a constitution save or get a piece of pure darkness lodged inside of it. In 1 round the darkness solidifies into talons that begin to rip at the creature's insides. Every round after that, the creature must make a constitution saving throw or take 2d8 necrotic damage (half on a passed save). Every time it takes full damage, it must make another constitution save or be incapacitated for the rest of the duration. 

For every spell slot level after the 3rd the damage increases by 2d8.