All Pokemon introduced after XY are banned. All Pokemon that existed in XY are banned unless they are flying type, have levitate, or are Bronzor or Bronzong.
These flying Pokemon are banned: Spearow, Farfetch'd, Doduo, Dodrio, Hoothoot, Natu, Murkrow, Delibird, Taillow, Starly, Chatot, Shaymin, Pidove, Archen, Ducklett, Rufflet, Vullaby, Fletchling, Hawlucha
These levitate Pokemon are banned: Gengar
Note that mega evolving any allowed Pokemon is allowed, even if the mega evolution loses the flying type or levitate. Also stuff like mega Pinsir is banned because it has to start as a non-flying type.