Galvantula crest: Sets a layer of sticky webs upon entry and brings all flying pokemon to ground (based on its pokedex entry)
Braviary crest: Sky Drop becomes a one-turn move, gains moxie ability
Gogoat crest: Increases HP gain from recovery moves, contact (or horn) moves are buffed.
Dragalge crest: Increases speed in rain or when underwater, all moves have a chance to poison.
Clawitzer crest: either increases speed in rain or underwater, or just a boost to the base speed, sniper ability is added.
Noivern crest: gains punk rock, normal moves become flying or dragon.
Toxitricity crest: increase in speed when hit by opposing sound moves, normal moves become poison type.
Alright thats it for my second round of suggestions lol