This is exactly what it sounds like. Changes: Pokemon typings are as they would be in Gen 6. Existing moves that become Fairy type in Gen 6 are Fairy type. New moves from Gen 6 won't be added. Mewtwo's new form won't exist, since it's not in gen 5. I can't remember what Fairy types are weak or strong against, but I'm sure they've revealed it already. These above rules aren't set in stone, so if they seem unreasonable I'm willing to compromise.