That actually may not be a bad idea. My first thought was to focus the deck almost entirely around getting Shrine of Memories out and using Damage Change with the mega. In that case, I'm not sure how well fairy energy fits. But now that you've mentioned Xerneas, I think it may be possible to build a deck around Psychic Infinity with it and Clawitzer.
In an ideal situation, you could have an M Mewtwo ready to swing for 160 on turn two, not counting your opponent's energies. Depending on how lucky you get and how long it takes your opponent to knock out a starting Xerneas, it's conceivable that you could be swinging for 250 + opponent's energies by turn 3. It would be a fairly risky strategy, but that sounds like something that would be incredibly fun to pull off.