Devouring Shadow

The target must be incapacitated or dead. The target must make a Constitution saving throw. Dead targets automatically fail. 

Upon failure the shadows of the Dark Power cover the target. They are then absorbed into the casters own shadow. Upon absorption the target is placed in a limbo like state where time is irreverent. The target is taken out of turn order and doesn't make Death saving throws. The target is kept in the shadow for 24 hours or until the caster chooses to dispel the target. If the caster loses concentration the target reappears in an empty adjacent position to the caster.  

Upon success, the target resists the spell.