Ice Walk. The dragon 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 it extra movement.

Multiattack. The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage plus 4 (1d8) cold damage plus 6 (1d10) lightning damage. 

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

Cold Lightning Breath (Recharge 5–6). The dragon exhales an sparky icy blast in a 30-foot cone. Each creature in that area must make a DC 15 Constitution saving throw, taking 45 (5d8) cold damage on a failed save, or half as much damage on a successful one. Plus a additional 55 (5d10) lightning damage on a failed save, or half as much damage on a successful one.