Corrupted Phoenix Servant

Magic Resistance. The corrupted phoenix servant has advantage on saving throws against spell sand other magical effects.

Illumination. The elemental radiates bright light for 20ft and dim light for an addition 20ft. 

Fire Form. The elemental can pass through a hole up to a hole that is 1 inch wide or larger. When they pass through a person, they deal 5 (1d10) fire damage + 2 (1d4) necrotic damage.

Pack Tactics. Advantage on attack rolls against creatures within 5 ft of its ally. The ally cannot be incapacitated.

Multiattack. With this action, the elemental can make 1 bite attack and 2 claw attacks.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 11 (2d6 + 5) piercing damage and 4 (2d4) necrotic damage. The target must then make a DC 15 Dexterity saving throw or take 5 (1d10) fire damage at the start of each of their turns until the fire is put out. 

Claw. Melee Weapon Attack: +8 to hit, range 5 ft., 1 target. Hit:  8 (1d6 + 5) piercing damage, 2 (1d4) fire damage, and 2 (1d4) necrotic damage.

Fire Breath of Death. 15 ft. cone of dark fire. Each creature within the cone must make a DC 15 Dex save or take 10 (2d10) fire damage and 8 (2d8) necrotic damage (reduces max HP) on a failed save or half as much on a successful one.

Superior Invisibility. As a bonus action, they can turn invisible. This ends when they fail a Constitution saving throw (+1) that is DC 10 or half of the damage they took, whichever is higher.