Abbodon

Demonic Restoration. If Abbodon dies outside the Abyss, its body dissolves into ichor, and it gains a new body instantly, reviving with all its Hit Points somewhere in the Abyss.

Magic Resistance. Abbodon has Advantage on saving throws against spells and other magical effects.

Multiattack. Abbodon uses Possession, then makes three Rend attacks.

Possession. Wisdom Saving Throw: DC 15, one creature within 60ft. that Abbodon can see. Failure: The target is Charmed for 1 minute. While charmed in this way, the target is entirely controlled by Abbodon and will act on its will alone. The target can remake this saving throw at the end of each of its turns, ending the effect on a success.

Rend. Melee Attack Roll: +10, reach 10ft. Hit: 16 (2d10 + 5) Slashing damage plus 11 (2d10) Necrotic damage.

Teleport. Abbodon teleports up to 120 feet to an unoccupied space it can see.

Horror Nimbus (Recharge 5–6). Wisdom Saving Throw: DC 15, each creature in a 15-foot Emanation originating from Abbodon. Failure: 28 (8d6) Psychic damage, and the target has the Frightened condition for 1 minute, until it takes damage, or until it ends its turn with  out of line of sight. Success: The target is immune to the Horror Nimbus for 24 hours.

Pursuit. Trigger: Another creature  can see ends its move within 120 feet of it. Response: Abbodon uses Teleport, but its destination space must be within 10 feet of the triggering creature.