The other one is based on @rarefaction ‘s awesome idea (so credit to them!) that Mimikyu’s second evolution would just be Mimikyu without the Pikachu disguise! The trainer makes Mimikyu appreciate itself for what it is!
And the other one is my idea - Mimikyu doesn’t learn to love itself and the grudge and sadness is just too much. It turns into an angry and bitter monster, who’s powerful but very alone. :[