I came up with his while trolling a friend who is super eager for this games' release.
Mewtwo's new form has a signature move that, on hit (standard accuracy) will drop the enemy's health into 1 HP. Thing is, the move will only work if Mewtwo is holding a species-specific item that randomizes his attacks, so you can't choose your moves. Every move has an equal 25% chance of being deployed. The item will not work if Mewtwo has less than 4 moves. What's more, Mewtwo has also a neat ability, which works as follows: "If Mewtwo defeats a Pokémon having resourced to the aforementioned signature move, the next incoming Pokémon will have his moves randomized for 5 turns".
Also, on an unrelated note, I would love to see a new status move that makes the enemy Pokémon de-evolve. Imagine, if you will, a move with an Yawn-like mechanic, in which one turn after using the move, the target would go back into his former evolutionary stage. On switch, the Pokémon is returned back to normal, and, with every turn, the pokémon would go back one stage.
"Gosto de todos, menos do Ramiro, que e repetente" - Bruno Aleixo
We could just make false swipe 200 bp, no need to make things so complicated. As far as devolution goes it's also an overly complicated way of making a pokemon weaker why not just have a move opposite to ancient power with a 1 in 10 chance of lowering all of your opponents stats by 1 stage