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.
The dragon makes two Rend attacks.
plus 2 (1d4) Cold damage.
Constitution Saving Throw: DC 12, each creature in a 15-foot Cone. Failure: 22 (5d8) Cold damage. Success: Half damage.