Ancient Phoenix

Keen Sight. The Phoenix has advantage on Wisdom (Perception) checks that rely on sight.

Fire Resistance. The Phoenix is born with a natural fire resistance.

Innate Spellcasting. The Phoenix’s spellcasting ability is Charisma (spell save DC 18). The Phoenix can innately cast the following spells, requiring no components:

At will: Fireball, wall of fire 1/day each: Fire storm 3/day each: Delayed blast fireball, meteor swarm.

Multiattack. The Phoenix makes two attacks: one with its beak and one with its talons.

Beak. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) piercing damage.

Talons. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) slashing damage.

Fireball. Ranged Weapon Attack: +20 to hit, range 30 ft., two targets. Hit: 15 (2d20 + 8) burning damage.

Burning Talons. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 12 (1d20 + 5) burning and slashing damage.

Blazing Hide. Melee Weapon Attack: +20 to hit, reach 1 ft., five targets. Hit: 15 (2d20 + 5) burning damage.

Flaming Multiattack. The Phoenix makes three attacks two with it’s talons and one with fireball.  

If the Phoenix is reduced to 50 or lower hit points it can use burning hide and  flaming mutiattack at the same time even when it isn’t it’s turn, (once a round).

Legendary Resistance (3/day). If the Phoenix fails a saving throw, it can choose to succeed instead.

Immortality. Every 500 years the Phoenix burns itself to ashes and is reborn as a egg. It still can remember every thing from it’s old life, though.