M mewtwo is nice in that it's energy requirement for Psychic Infinity is colorless, so it pairs easily with many things. I'm a fan of a Zoroark/Yveltal pairing myself. 2-2 Zoroark line, 2 Yveltal EX, and one each of the baby bacon birds. I round those and 3-3 M Mewtwo line out with 2 Shaymin EX and a Hoopa EX for good bench filling support.
For supporters, the standard Sycamore/N/Trainers Mail/Ultra ball core is a must, along with 3 spirit links, a skyla maybe for item finding, and some other supporters like Lysandre/Hex maniac/Pokemon ranger to deal with nuisance on the board.
Energy wise, darkness and DCEs fit the bill nicely.
Hope you find this helpful!