Articuno

Frigid Body. Articuno’s body is incredibly cold, causing moisture in the air to freeze into snow as it beats its wings. Creatures that start their turn within 15 ft. of Articuno take 9 (2d8) cold damage. 

Snow Cloak. If Articuno ends its turn under a snowstorm and it did not attack or cast a spell this turn, it becomes invisible. When Articuno attacks or casts a spell, or if it exits the snowstorm’s area, this invisibility ends. 

Flyby. When Articuno hits a creature with a melee attack, it can leave that creature’s reach without provoking an opportunity attack.

Legendary Resistance (3/Day). When Articuno fails a saving throw, it can choose to succeed instead. 

Innate Spellcasting. Articuno is an innate spellcaster. Wisdom is its spellcasting ability (Spell Save DC 19, +11 to hit with Spell Attacks). Articuno can cast the following spells, requiring no material components:

At Will: Gust of Wind, Sleet Storm

3/day Each: Mirror Image, Ice Storm

1/day: Wall of Ice

Multiattack. Articuno uses Blizzard if available, then makes 3 attacks with Talons, or two attacks with Ice Beam.

Talons. Melee Weapon Attack: +10 to hit, reach 5 ft., 1 target. Hit: 14 (2d8 + 5) slashing damage and 9 (2d8) cold damage. 

Ice Beam. RangedWeapon Attack: +11 to hit, range 120/400 ft., 1 target. Hit: 27 (5d10) cold damage and the target’s speed is reduced by 10 feet. A creature can make a Constitution saving throw (DC 18) to end this effect on itself. This effect can stack multiple times, reducing the target’s speed until it reaches 0, at which point the target is frozen in ice and considered paralyzed. One successful save ends all stacks of this effect.

Blizzard (5-6). Articuno beats its wings furiously, whipping the air around it into a storm of freezing wind carrying blades of sharp ice. All creatures within 60 ft. of Articuno make a DEX saving throw (DC 19). A creature takes 22 (5d8) piercing damage and 22 (5d8) cold damage on a failed save, or half as much on a success. Additionally, the area within a 120 ft. sphere around Articuno becomes a snowstorm for 1 minute if it wasn’t already.

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

Wingbeat. Articuno moves up to half its speed without provoking opportunity attacks, and any creatures it passed through the reach of take 18 (4d8) cold damage.

Talons (Costs 2 Actions). Articuno makes an attack with its Talons.

Ice Beam (Costs 2 Actions). Articuno makes an Ice Beam attack.