Snow Cloak is an ability introduced in generation 4.
11 Pokémon can have this ability, such as Swinub, Piloswine, Glaceon, Mamoswine and Froslass. For 1 of them it is the hidden ability, usually obtained from events, raids or breeding.
Official effect
Increases evasion to 1.25× during hail. Protects against hail damage.