Ice glide.  Can meld into and glide threw Ice and snow and move 80ft.  While melded in the ice the winter serpent can hide as a bonus action.  Any creature attempting to find it while it is melded in ice can do so at a disadvantage. 

Ice Venom Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 7 (1d6 + 4) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 18 (3d8) cold damage on a failed save, or half as much damage on a successful one. After bitten you take half of the damage of the ice venom damage every subsequent round at the beginning of the creatures turn. A lesser Restoration  or Remove poison is required to remove the poison. All ice venom damage will lower your max hit points until the ice venom is removed. If your hit points reach 0 you turn into a statue of ice.  A greater restoration will restore the ice statue back into normal form bringing the creatures back this way will restore them to one hit point.

Snow Flurry. Once per round as a reaction the winter serpent can turn into snow flurry  and take half damage to the attack.