Monastery of the Distressed Body Grand Master

Shards of a vorpal sword once broken against the devil replace its claws. A successful DC 12 Intelligence (Arcana) or Wisdom (Perception) check identifies them as such. When the devil rolls a 20 on an attack roll with a claw, the target is decapitated. (At your option, the attack can instead deal an extra 6d8 slashing damage.) A target is immune to this effect if it is immune to slashing damage, has legendary actions, doesn't have or need a head, or if you decide that the target is too large for its head to be cut off by the devil's claws. If removed, the shards lose their magical powers.

Local teleportation-field bracelets encircle the devil's arms and tail. These devices allow the Grand Master to make its claw and sting attacks remotely, though still on the devil's turn and using its actions.

Magical darkness doesn't impede the Grand Master's darkvision.

The Grand Master has advantage on saving throws against spells and other magical effects.

The Grand Master makes three attacks: two with its claws and one with its sting.

Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 8 (1d8 + 4) slashing damage.

Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) piercing damage plus 17 (5d6) poison damage, and the target must succeed on a DC 14 Constitution saving throw or become poisoned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.