Dark Seal

You command shadows to surge upward and bind a creature within range, forming a writhing cocoon of darkness that constricts and seals. The target must make a Charisma saving throw (Spell DC + your charisma modifer). On a failed save, it becomes restrained as shadowy bindings envelop its body and partially drag it into a shadowy pocket dimension. On a success, the spell fails. While restrained in this way, the target is blinded and deafened, and it takes 5d8 necrotic damage at the start of each of your turns as the shadows constrict and feed on its essence.

At the end of each of its turns, the target can repeat the Charisma saving throw, ending the effect on a success. If the target remains sealed for the full duration, the shadows attempt to fully consume it. The creature must make one final Charisma saving throw: On a failure, it takes 10d10 necrotic damage and is banished into a shadowy demiplane until the end of your next turn. On a success, it takes half damage and is not banished. If the creature is reduced to 0 hit points while sealed, its body dissolves into shadow.