Spinel

I have another suggestion maybe not too well thought but it was an interesting one to share atleast. Donphan crest : If it uses a spin or ball move it gets +1 speed. If gyro ball is used it does max dmg. If rapid spin Is used the +1 speed is changed to +1 Def and gets the +1 speed from Gen 8 rapid spin (I thought of this mostly due to how donphan is usually spinning like a ball, and also due to the stadium 2 mini game.)

Another set of ideas i had and tried to made well. with the help of both Moto and SG. Heliolisk Crest: solar power but for rain, leaf guard in sun, sand force in sand Golduck crest: using psych up with golduck crest confuses you and you get +1 sp attack each turn you are confused (Reference to the dex entries + a more reliable way to get confused) Persian Crest: gains a crit stage increase if it's faster than the target + Sniper ( To resemble a bit the old crit mechanics) Crabominable Crest : Reduces Dmg from fire atks by 0,3% and if hit by a SE move the target will be bind for 3 turns ( a bit of a buff to survive fire moves due to its heavy fur and a reference to the dex with the pincers that can be thrown )

Some ideas i had for some mons that have niches but are mostly outclassed and such. Sandslash Crest: After using a Ground or Steel Type move , the mon gains an effect like gulp missile but with -1 speed on hit. (Mostly a reference to how the spikes of and claws of Sandslash can fall off) Alolan Sandlash Crest : The mon gains a 20% chance of freezing if a mon makes contact with him ( Reference to the pokedex entries too) Poliwrath Crest: Gives Water moves priority if the mon Hp is above 75% Politoed Crest: Dry Skin effect