Anivia, The Cryophoenix

Icy Death and Rebirth. When Anivia dies, she explodes. Each creature within 60-feet of her must make a DC 20 Dexterity saving throw, taking 24 (4d10) cold damage on a failed save, or half as much damage on a successful one. The ice flash freezes objects in the area that aren’t worn or carried.

The explosion destroys Anivia’s body and leaves behind an egg-shaped glacial chunk that weighs 70 pounds. The egg is cold like True Ice, dealing 24 (6d6) cold damage to any creature that touches it, though no more than once per round. The egg is immune to all damage, and after 1d6 days, Anivia hatches fully matured, reborn anew.

True Ice Form. Any creature that touches Anivia or hits her with a melee attack while within 5 feet of her takes 5 (1d10) cold damage. With a touch, Anivia can also flash freeze objects that aren’t worn or carried (no action required). Anivia's attacks ignore Immunity to cold damage.

Flyby. Anivia doesn’t provoke opportunity attacks when she flies out of an enemy’s reach.

Legendary Resistance (3/Day). If Anivia fails a saving throw, she can choose to succeed instead.

Siege Monster. Anivia deals double damage to objects and structures.

Multiattack. Anivia makes two attacks: one with her beak and one with her frozen talons. Anivia may replace one attack with a Frostbite.

Beak. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 15 (2d6 + 8) cold damage. Targets hit are covered in biting frost, their movement speeds are reduced by 10 until the end of their next turn.

Frozen Talons. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) cold damage.

Flash Frost (Recharge 5-6). Anivia launches a massive chunk of ice toward a point within 100 ft. of her, bursting on impact. Creatures within 15 ft. of the point must succeed on a DC 20 Dexterity saving throw, taking 32 (8d6) cold damage on a failed save, or half as much damage on a successful one. A creature that fails the save by 5 or more is incapacitated until the end of its next turn as frost builds up on them, preventing proper range of motion.

Crystallize (Recharge 6). Anivia erects a wall of ice.

Frostbite. Anivia blasts the target with a freezing wind and ice. Ranged Weapon Attack: +13 to hit, range 40/100 ft., one target. Hit: 18 (2d8 + 8) cold damage.

Glacial Storm (1/rest). Anivia calls forth a storm of ice and hail in a 120 ft. radius centered on a point she can see. The storm lasts for 1 minute. Creatures that move into the storm or start their turn within must succeed on a DC 20 Dexterity saving throw, taking 48 (12d6) cold damage on a failed save, or half as much damage on a successful one. A creature that fails the save by 5 or more is incapacitated  and its movement is reduced to 0 until the start of its next turn.

Anivia 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. Anivia regains spent legendary actions at the start of her turn.

Peck. Anivia makes one beak attack.

Move. Anivia moves up to her speed.

Swoop (Costs 2 Actions). Anivia moves up to her speed and attacks with her frozen talons.

Moving Maelstrom (Costs 3 Actions). Anivia moves her Glacial Storm 40 ft..

Shifting Tundra (Costs 3 Actions). Anivia moves her wall of ice to new point within 40 ft. of her.