There should be one more MV

[Total: 1    Average: 1/5]

[X]

The specifics aren’t 100% clear here, but it would appear that you need to train up a particular Pokémon to then challenge the master of that very same Pokémon (who will also battle with that Pokémon), and you’ll need to do this 151 times if you want to be the champion of everything the game has to offer. Masuda did go on to suggest that this might be the only real post-game content, other than grabbing Mewtwo and completing your entire Pokédex, of course, but it sounds like a rather substantial undertaking.