Pokémon X and Pokémon Y

But wait, isn't Mewtwo's base speed a lot higher in the game than Genesect's? Whatever, not all game stuff applies to the anime anyway. (Curse the writers for failing hard when it comes to Colress's "mad scientist" side)

It's actually worse than it sounds. Mewtwo is already tied for 7th fastest pokemon in the entire game. And, that's counting 3 of deoxys forms (Attack, Normal, Speed) as seperate pokemon. Only electrode, ninjask, deoxys and accelgor are faster.

Mewtwo is one of the last pokemon that needs a speed boost really.