FINALLY got around to getting art of my mewtwo gal, Psy. Thanks a ton to Rubbermage for drawing this.

As for backstory, its the same as normal mewtwo's, at least at its core, but where it differs is in the extent through which the experimentation and the power amping was done. This mewtwo wasn't designed just to be an incredibly strong pokemon. She was designed to be the absolute strongest. And as her creation is rather recent (she was created in Alola), word of Arceus was already abound. And as such, she was worked on, experimented on, and tortured (experiments can get pretty gruesome when you're working with a being you believe to be just a synthetic creation and not a real living thing). As such, when she finally escaped, it didn't just flatten the entire laboratory where she was being held, nay, the energy she shot skyward flattened the entire Island (luckily it wasn't one of the main ones), created 50 foot tall waves, and shown a beam that could be seen clearly from several hundred miles in all directions.

Mewtwo © Gamefreak
Art by  Rubbermage