Hey so I have made a big mod that included adding a ton of crests into the game, I'll just copypaste the list of the ones I have made already. Note that a lot of these are very OP because they are used by the enemy trainers in my mod, and it's meant to be very difficult.
Beautifly Crest - Multiplies Sp. Attack by 1.1. Gives you the effects of Gale Wings and Technician.
Dustox Crest - Multiplies Sp. Defense by 1.3. Sp. Attack now scales off of Sp. Defense. Poison type attacks used by Dustox are now super effective against Steel types.
Drampa Crest - Makes Drampa faster the