Crismon Coffin

You use the dark arts of blood magic to immobilize your enemies.

You make a melee spell attack against the chosen creature, the target has to make a strength saving throw or be imprisoned in a coffin of crimson blood, under the grappled condition. The coffin has a AC of 10 + spell casting modifier and a HP of spell level + casters level + 2d6. 

Each round a creature is in the coffin it takes 1d6 necrotic damage that heals the caster.