The Pokémon Global Link has posted a survey for player to choose the format for an upcoming Online Competition. There are five competitive formats to choose from. Players can choose one of the formats in the survey.

Pokémon Global Link November 2015 Online Competition Survey Formats

No Mega: Mega Stone held items are prohibited.
Inverse Double Battles: All type matchups are reversed.
Anything Goes: Triple Battles in which multiples of any and all Pokémon and items are permitted (including Pokémon brought over via Poké Transporter).
Anti-Evolution: Only Pokémon that can’t evolve and haven’t evolved are permitted. (Mega Evolution does not count as having an Evolution.) All Legendary and Mythical Pokémon are banned.
Underdogs: Pokémon that finished among the top 12 in any 2015 Double Battle Online Competition are banned.

Source: http://3ds.pokemon-gl.com/information/16875eae-b229-459a-9fd7-d263c52a9809