Not75Drops
Member
http://www.pokemon.com/us/strategy/vgc-2016-champion-series-preview/
http://www.pokemon.com/us/pokemon-news/the-2016-video-game-championship-format-has-been-announced/
Note that Legendary Pokemon don't include Mythical Pokemon, which are event-only (except Deoxys)
Looks like that means Mega Rayquaza is allowed.
http://www.pokemon.com/us/pokemon-news/the-2016-video-game-championship-format-has-been-announced/
-All battles will be Double Battles played in Pokémon Omega Ruby and Pokémon Alpha Sapphire.
-Time limits for battles will vary by event. At major events (Regional Championships and above), battles will have a 15-minute time limit, 45-second move timer, and a 90-second Team Preview.
-Pokémon brought in via Poké Transporter will not be permitted (the blue pentagon is required).
-All discovered Pokémon will be allowed except the following Mythical Pokémon: Mew, Celebi, Jirachi, Deoxys, Phione, Manaphy, Darkrai, Shaymin, Arceus, Victini, Keldeo, Meloetta, Genesect, Diancie, and Hoopa.
-Teams may have no more than two of the following Pokémon: Mewtwo, Lugia, Ho-Oh, Kyogre, Groudon, Rayquaza, Dialga, Palkia, Giratina, Reshiram, Zekrom, Kyurem, Xerneas, Yveltal, and Zygarde.
-All items will be allowed except Soul Dew. Each Pokémon must hold a different item.
Note that Legendary Pokemon don't include Mythical Pokemon, which are event-only (except Deoxys)
Looks like that means Mega Rayquaza is allowed.