The Gym Leader Challenge is a casual format where you and your opponent master a single type of Pokemon using an extended list of legal cards beyond the standard format
As long as this Pokmon is in the Active Spot, it can evolve during your first turn or the turn you play it
Her abilities dont stack in any useful way and we cant use her activated ability
Sources: TCG Player (Base Set Mewtwo, First Edition Rocket's Mewtwo, Mew & Mewtwo GX, Mewtwo ex, Mewtwo Gold Star, Rocket's Mewtwo ex, Shining Mewtwo, Mewtwo e-Card, Rocket's Mewtwo [Winner], Mewtwo [XY Evolutions Staff Prerelease]), PriceCharting (Base Set 1st Edition Shadowless Holo Mewtwo, Mewtwo Gold Star)
This is a great card to unload on your foe
Wizards of the Coast president Cynthia Williams revealed that Final Fantasy and Assassins Creed will join the game via its Universes Beyond initiative allowing MTG to include characters and such from outside of its own realms