Alert.The xixecal gains a +5 bonus to initiative rolls. The xixecal can't be surprised while conscious, and other creatures don't gain advantage on attack rolls against it as a result of being unseen by it.

Immutable Form. The xixecal is immune to any spell or effect that would alter its form.

Innate Spellcasting.The xixecal's innate spellcasting ability is Charisma (save DC 23, +15 to hit with spell attacks). The xixecal can cast the following spells, requiring no material components

At will: dispel magic (as a 5th-level spell), dominate monster, elemental bane (cold; as a 9th-level spell), greater invisibility, hold monster, nondetection (self only), wall of ice
5/day: haste
1/day: meteor swarm

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

Living Storm. The xixecal is always at the center of a blizzard 5 miles in diameter. Heavy precipitation in the form of snow or hail falls there, causing the area to be lightly obscured. Strong winds swirl in the area covered by the storm. These winds extinguish open flames, disperse fog, and impose disadvantage on both Wisdom (Perception) checks that rely on hearing and on ranged attack rolls.

Magic Resistance. The xixecal has advantage on saving throws against spells and other magical effects.

Magic Weapons. The xixecal's weapon attacks are magical.

Regeneration. The xixecal regains 30 hit points at the start of its turn if it has at least 1 hit points remaining. If the xixecal takes fire damage, this trait doesn't function at the start of its next turn.

Siege Monster. The xixecal deals double damage to objects and structures.

Multiattack. The xixecal makes two claw attacks.

Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 24 (4d6 + 10) slashing damage plus 18 (4d8) cold damage, and the target must succeed on a DC 23 Constitution saving throw or be slowed for 1 minute, as if affected by the slow spell. A creature can repeat the saving throw at the end of each of its turns, ending the effect on a success.

Cold Breath (Recharge 4-5). The xixecal exhales an icy blast in a 120-foot cone. Each creature in that area must make a DC 23 Consitution saving throw. On a failed save, a creature takes 90 (20d8) cold damage and is slowed for 1 minute, as if affected by the slow spell. A creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. A creature that succeeds on the initial saving throw takes half as much damage, and is not slowed.

Summon Dragon (Recharge 6). The xixecal summons one ancient white dragon which materializes within 60 feet of it in an unoccupied space it can see. Dragons summoned by this effect cannot use any legendary actions. The dragon obeys its summoner's commands and can't be controlled by any other creature. The dragon vanishes when it drops to 0 hit points or when its summoner dies.

The xixecal 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. The xixecal regains spent legendary actions at the start of its turn.

Attack. The xixecal makes one attack.
Stomp (Costs 2 Actions). The xixecal stomps the ground, creating a tremor. This functions as an earthquake spell centered on the xixecal (save DC 23). The effect lasts only until the end of the xixecal's next turn, and the xixecal automatically succeeds on all saving throws against its own earthquake.
Absolute Zero (Costs 3 Actions). The xixecal completely absorbs all heat from the immediate vicinity, causing the temperature to plunge as low as possible (about -273 degrees Celsius or -459 degrees Fahrenheit). All creatures within 120 feet of the xixecal that are not immune to cold damage must succeed on a DC 23 Constitution saving throw or gain one level of exhaustion. Creatures resistant but not immune to cold damage make this saving throw with advantage.