Tried to be creative for a few mons
Aegislash Crest: Ghost-type and Steel-type attacks become super-effective against Dark-types. When King's Shield is used and blocks an attack (either physical or special), the attack is reflected back at the opponent for half damage.
Mr. Rime Crest: Becomes immune to sound moves, but when hit by one, it gains the Screen Cleaner ability effect and its speed and special attack are boosted. All effects are removed after the end of the turn.
Arctozolt/Arctovish Crest: Once sent out, the Pokémon acts if it is in trick room (If it's the slowest on the field it is the fastest and vice versa), but all other Pokémon function as normal (Fastest moves first). Base speed is decreased by 20.
Cryogonal Crest: Once sent out, it activates the hail like the ability Snow Warning. All Ice-type moves it uses become super effective against Water-types and have a 20% chance to freeze on all types except Ice-types.
