Chained Angel

Immortal Nature. The chained angel doesn't require food, drink, or sleep.

Magic Resistance. The chained angel has advantage on saving throws against spells and other magical effects.

Redemption. When a creature casts the knock spell on the chained angel's chains, the chains release a blast of unholy flame. The spellcaster must make a DC 16 Dexterity saving throw, taking 16 (3d10) fire damage and 16 (3d10) radiant damage on a failed save, or half as much damage on a successful one. If the spellcaster survives, the chained angel must immediately make a DC 17 Wisdom saving throw. On a success, the angel's chains fall away. It is restored to its senses and the form it had before it was chained, typically a deva. On a failure, the chained angel remains chained for 7 days, and during that time, any further attempts to cast knock on the angel's chains fail.

Multiattack. The chained angel makes two Fiery Greatsword attacks.

Fiery Greatsword. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage plus 16 (3d10) fire damage.

Fallen Glory (Recharge 5-6). Each creature the chained angel can see within 50 feet of it must make a DC 15 Strength saving throw. On a failure, a creature takes 19 (3d12) radiant damage and is knocked prone. On a success, a creature takes half the damage and isn't knocked prone.

Fiendish Cunning. When a creature the chained angel can see within 60 feet of it casts a spell that appears on the cleric or paladin spell list, the chained angel can counter the spell with a successful ability check. This works like the counterspell spell with a +5 spellcasting ability check, except the chained angel must make the ability check no matter the level of the spell.