Cinder Phoenix

Fire Form. The elemental can move through a space as narrow as 1 inch wide without squeezing. A creature that touches the elemental or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage. In addition, the elemental can enter a hostile creature's space and stop there. The first time it enters a creature's space on a turn, that creature takes 5 (1d10) fire damage and catches fire; until someone takes an action to douse the fire, the creature takes 5 (1d10) fire damage at the start of each of its turns.

Hellfire Aura. A creature that starts its turn within 5 feet of the Phoenix takes 5 (1d10) fire damage, and ranged attacks that target the Phoenix or pass through its 5-foot aura are reduced by 4 (1d8) damage (This feature is negated until the start of its next turn if the Cinder Phoenix is attacked with cold damage totaling to 5 or more)

Illumination. The elemental sheds bright light in a 60-foot radius and dim light in an additional 50 feet.

Water Susceptibility. For every 5 feet the elemental moves in water, or for every gallon of water splashed on it, it takes 5 cold damage.

Rejuvenation. After the Cinder Phoenix dies, it fades to ash and returns to the Elemental Plane of Fire with all of its hit points. If it dies in the Elemental Plane of Fire it turns to ash and returns in 1d4 days. This trait will not take place if the phoenix is destroyed with cold damage totaling 20 or more. 

Multiattack. The Phoenix can use its Blinding Presence. It then makes two touch attacks

Blinding Presence. Any creature within 200 ft of the Phoenix, that can see it,  must succeed on a DC 16 Wisdom saving throw or become blinded for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the phoenix's Blinding Presence for the next 24 hours.

Touch. Melee Weapon Attack:  reach 5 ft., one target. Hit: 10 (2d6 + 3) fire damage. If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.

The phoenix can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The phoenix regains spent legendary actions at the start of its turn.

Scorched Earth. The phoenix ignites the ground around it in a 5ft radius. This fire lasts for 1 round, and any creature who starts or enters this area takes 5 (1d10) fire damage. 

Flying Cinders. The phoenix beats its wings and kicks up debris, igniting it and slinging it at its foes. Up to three creatures within 100 ft can be targeted and must succeed on a DC 16 Dex saving throw and take 5 (1d10) slashing damage and 4 (1d8) fire damage on a failed save, or half as much on a successful save.

Diving Whirlwind (Costs 2 Actions). The phoenix beats its wings and dives along the ground in a straight line up to half its flying speed. Each creature within 10 feet of the phoenix's path must succeed on a DC 16 Dexterity saving throw or take 13 (2d8) fire damage, or half as much on a successful save.