>>46202857UM was easy. Ultra Necrozma fight: Pixilated Hyper Beam to the face, ball.
PokeMMO is harder in general (level caps for gym fights, AI knows how to switch and got better movesets).
PokeMMO is an MMO, so I just started a new character and mailed myself the 'vees.
UM had been my first Pokemon game, played with some random mons till I could get an Eevee, then bred the whole set.