>>56955585Give it Slush Rush. The point of the Eeveelutions is their adaptability to new environment : being able to adapt to a snowy environment to get faster is exactly that. It wouldn't be that OP either, base 65 speed isn't too high knowing Cetitan has it with base 73 speed. Snow Warning makes way less sense, it's about summoning weather, not adapting to it.
Thick Fat could also technically work as it's a form of adaptation but it's a bit less relevant to Glaceon specifically.