Frozen Rebirth Instinct.
When the Hatchling is reduced to 0 hit points, it explodes in a burst of sub-zero energy, leaving behind a fragile egg of pure ice. One hour later, it reforms from the egg with 50 hit points unless the egg is destroyed (AC 10, HP 10, immune to cold damage).

Aura of Bitter Cold.
Any creature that starts its turn within 20 feet of the Hatchling must make a DC 15 Constitution saving throw, taking 9 (2d8) cold damage on a failed save or half as much on a success.

Unstable Cry (Recharge 5–6).
The Hatchling releases an unbalanced screech of proto-elemental power. Each creature of its choice in a 30-foot cone must make a DC 15 Constitution save or take 22 (4d10) cold damage and be restrained by ice until the end of the Hatchling’s next turn. On a success, they take half damage and aren’t restrained.

Young Memory.
The Hatchling has flashes of ancient wisdom from its past lives. Once per day, it can add +1d6 to any saving throw, attack roll, or ability check. When it does, its eyes glow with aurora light for 1 round.

Feather of Frostfire – one of its feathers can be forged into a legendary weapon or artifact.

Multiattack. The falcon makes two Talon attacks and one Icy Breath (if available).

Talon. Melee Weapon Attack Roll: +7, reach 5 ft. Hit: 14 (2d8 + 4) Slashing damage plus 7 (2d6) Cold damage.

Icy Breath (Recharge 6).
The Hatchling exhales a cone of freezing air 30 feet long. Each creature in the area must make a DC 15 Constitution saving throw, taking 36 (8d8) cold damage on a failed save, or half as much on a success. Creatures who fail are slowed (as the Slow spell) until the end of their next turn.