Cryovain of Icespire (Young White Dragon, Increased Threat)

Ice Walk. Cryovain can move across and climb icy surfaces without needing to make an ability check. Additionally, difficult terrain composed of ice or snow doesn't cost her extra movement.

Legendary Resistance (1/Day). If Cryovain fails a saving throw, she can choose to succeed instead.

Winter's Wrath (Recharges after a Short or Long Rest). If Cryovain is reduced to 0 hit points, she doesn’t die or fall unconscious. Instead, the cold magic within her body explodes from her wounds, coating her body in thick, heavy plates of icy armor. Her fly speed becomes 0, and she loses the Cold Breath action. She regains 60 hit points, her AC becomes 21, and she gains the Glacial Plates and Freezing Aura traits. Additionally, Cryovain can now use the options in the “Mythic Actions” section

Freezing Aura (mythic form only). Any creature that starts its turn within 15 feet of Cryovain takes 2 (1d4) cold damage and has its speed reduced by 10 feet.

Glacial Plates (mythic form only). Heavy plates of ice cover Cryovain's body in four sections: head, torso, arms, and legs. Each of the four sections have connective points in the plates that can be targeted by attacks that use attack rolls; each of these targetable areas have 17 AC, 15 HP, and vulnerability to Fire damage. Whenever a section of plates is reduced to 0 HP, it is destroyed, dealing 10 damage to Cryovain and reducing her overall AC by 1.

Multiattack. Cryovain makes three melee attacks: one with her bite and two with her claws, or she makes two ice spike attacks.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage plus 4 (1d8) cold damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Ice Spike. Ranged Weapon Attack: +5 to hit, reach 100/200 ft., one target. Hit: 6 (1d6 + 3) piercing damage. Hit or miss, the spike then explodes. The target and each creature within 5 feet of it must succeed on a DC 15 Dexterity saving throw or take 4 (2d4) cold damage.

Cold Breath (Recharge 5–6). The dragon exhales an icy blast in a 30-foot cone. Each creature in that area must make a DC 15 Constitution saving throw, taking 45 (10d8) cold damage on a failed save, or half as much damage on a successful one.

Cryovain can take 2 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. Cryovain regains spent legendary actions at the start of her turn.

Attack. Cryovain makes a single claw attack.

Tail Flick. Cryovain makes a single ice spike attack.

If Cryovain’s Winter's Wrath trait is active, she gains one additional legendary action (to a total of 3), and can use the options below as a legendary actions, as long as she still has armor from her Glacial Plates trait.

Cold Snap. Cryovain slams an armor-plated part of her body into the ground, sending a wave of cold magic towards a creature she can see within 120 feet that is standing on the ground. The ice erupts around the creature, and it must succeed on a DC 15 Dexterity saving throw or become restrained to the floor by ice. A creature can use its action to make a DC 15 Strength check, freeing itself or another frozen creature within reach on a success. The ice can also be attacked and destroyed (AC 15; HP 10; vulnerability to fire damage; immunity to cold, poison, and psychic damage).

Flash Freeze (Costs 2 Actions). Cryovain emits a burst of cold energy from the wounds on her body, freezing and damaging every creature within a 15-foot radius centered on herself. Each creature in the radius must succeed on a DC 15 Constitution saving throw, taking 9 (3d6) cold damage on a failed save, or half as much damage on a successful one.