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

Frost Sense.
The frostfire dragon wyrmling can sense the presence of any creature within 120 feet of them that is in contact with freezing temperatures. This contact might be from that of snow, ice or simply frigid air.

Multiattack.
The frostfire dragon makes three attacks of any combination of bites and fire rays.

Bite.
Melee Weapon Attack: +10 to hit, reach 5ft., one target.
Hit: 15 (2d10+5) Piercing damage + 6 (2d6) Cold damage.

Fire Ray.
Ranged Weapon Attack: +10 to hit, range 150/600, one target.
Hit: 20 (5d6+5) Fire damage.

Frostfire Beam (Recharge 5-6).
The frostfire dragon wyrmling exhales a beam of frostfire in a 90-foot line that is 5-feet wide. Each creature in the line's area must make a DC 18 Dexterity saving throw, taking 61 (14d8) Fire (or Cold) damage on a failed save or half as much on a successful save.

Ice Sculptor (3/day).
The frostfire dragon casts the Fabricate spell as an action. The dragon can only target ice or snow when using this action and can fabricate a Huge or smaller object rather than one that is just large or smaller.

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

Move.
The frostfire dragon moves up to its speed.

Fire Ray.
The frostfire dragon makes a fire ray attack.

Frost Wing Attack (Costs 2 Actions).
The frostfire dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 18 Dexterity saving throw or take 9 (1d8+5) Bludgeoning damage and 4 (1d8) Cold damage and be knocked prone. The frostfire dragon can then fly up to half its flying speed.