Coldfire Phoenix

Flyby. The coldfire phoenix doesn't provoke opportunity attacks when it flies out of an enemy's reach.

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

Siege Monster. The coldfire phoenix deals double damage to objects and structures.

Cold Form. The coldfire phoenix radiates a cold energy around it. Any creature that touches the coldfire phoenix or hits it with a melee attack while within 5 feet of it takes 5 (1d10) cold damage.

Blizard Death. When the coldfire phoenix dies, it crystalizes into ice and shatters into thousands of shards. A blizzard forms, centered on the phoenix in a 1 mile radius. Each creature within 120 feet of the phoenix when it dies must make a DC 18 Constitution saving throw or take 20 (4d10) cold damage and 20 (4d10) slashing damage or half as much damage on a successful one. The blizzard is supernatural weather, lasting for 2d4 weeks.

Icy Rebirth. When the coldfire phoenix dies and shatters, the largest fragment contains the essence of the phoenix. If the fragment is left in the blizzard created, it creates a new coldfire phoenix after one week. Additionally, if a creature touches the shard and expends spell slots whose combined levels equal 13 or more, the shard creates a new coldfire phoenix in the space it was in.

 Innate Spellcasting. The phoenix's innate spellcasting ability is Wisdom (spell save DC19) It can innately cast the following spells requiring no material components. 

At will: Major image (5th level), Thaumaturgy.

3/day: Create or destroy water (creates or destroys up to 10 cubic feet of ice), Fog cloud, Silence (spell effect range 300 feet), Shatter

1/day: Ice Storm, Cone of Cold, Wall of Ice

Multiattack: The coldfire phoenix makes two attacks, one with its beak, one with its talons. 

Beak. Melee Weapon Attack: +13 to hit, reach 10 ft., 1 target. Hit: 15 (2d6 + 8) Piercing damage and 10 (2d10) cold damage

Talon. Melee weapon attack: +13 to hit, reach 10 ft., 1 target. 17 (2d8 + 8) Piercing damage and 10 (2d10) cold damage.

Cold Wind (Recharge 5-6). The coldfire phoenix lands and flaps its wings, causing cold air to rush in a 60 foot cone. Each creature in that area must make a DC 19 Dexterity saving throw or take 20 (4d10) cold damage and 20 (2d10) slashing damage  be frozen in place, reducing that creatures movement speed to 0 until the start of the phoenix's next turn. On a successful save, the creature takes half as much damage and its movement speed is reduced by half until the start of the phoenix's next turn.

The coldfire phoenix has 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 creatures turn. The coldfire phoenix regains spent legendary actions at the start of its turn.

Fragment. The coldfire phoenix hurls several dagger like feathers at a creature it can see within 120 feet. That creature must succeed on a DC 16 Dexterity saving throw or take 10 (2d10) and its movement speed is reduced by 10 until the end of the coldfire phoenix's next turn. On a successful save, the creature only takes half as much damage and its speed isn't reduced.

Burst of cold (Costs 2 Actions). The coldfire phoenix releases a burst of frigid air from its body. Each creature within 10 feet of it must succeed on a DC 18 Constitution saving throw or take 20 (4d10) cold damage. 

Icy Regeneration (Costs 3 Actions). The coldfire phoenix encases itself in a protective icy shell. While in the shell, the phoenix regains 1d12 hit points at the start of its turn. The shell has an AC of 12, 40 hit points and is immune to all damage except it is vulnerable to fire and bludgeoning. The shell lasts for three turns, until it is destroyed, or the phoenix ends the effect as a bonus action. While encased this way, the coldfire phoenix is unable to move or make an attack action.