The eleventh online competition for Pokémon Sun and Pokémon Moon has been announced. Mega Melee (メガランブル) will take place from Friday, September 22nd, 2017 at 00:00 UTC, through Sunday, September 24th, 2017, at 23:59 UTC.. Full details are listed below and on our 7th Generation Online Competitions page which will be updated as new tournaments are announced.

Mega Melee (メガランブル)

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Information
Region: International
Registration Period: Thursday, September 14th, 2017 at 00:00 UTC, through Thursday, September 21st, 2017, at 23:59 UTC.
Tournament Period: Friday, September 22nd, 2017 at 00:00 UTC, through Sunday, September 24th, 2017, at 23:59 UTC.
Ranking Results Announcement: October 2017
Player divisions: Junior/Senior Division: Born 2002 or later
Masters Division: Born 2001 or earlier
Junior/Senior Division players are limited to playing between 6 A.M. and 11 P.M., based on the easternmost time zone in each player’s country.
Compatible Games: Pokémon Sun and Pokémon Moon
Battle Type: Single Battle
Banned Pokémon: Eligible Pokémon are restricted to Pokémon that can Mega Evolve.
Entry Gift: Qualified participants will receive 50 Battle Points. To qualify, players must complete at least one battle.
Description
Get ready for epic battles with only Pokémon that can Mega Evolve in the Mega Melee Online Competition. Only one of the Pokémon from your team will enter battle, so pay close attention during the Team Preview and choose your Pokémon wisely! Duplicate Pokémon and items are not permitted, and every Pokémon will be set to Lv. 50 for the duration of these Single Battle clashes. The battles will take place in Pokémon Sun and Pokémon Moon, and Pokémon brought in via Poké Transporter are permitted in battle. The complete list of eligible Pokémon will be available in the competition regulations.

All qualified participants in the Mega Melee competition will receive 50 Battle Points. Players must complete at least one battle to qualify.
Competition Rules
• Mythical and Legendary Pokémon are not eligible.
• Duplicate Pokémon are not permitted.
• Duplicate items are not permitted.
• Items are permitted, including Mega Stones and Z-Crystals.
• Register three to six of your Pokémon to your Battle Team.
• All Pokémon in this competition will automatically become Lv. 50 for the duration of each match.
• Only one of the Pokémon you register to your Battle Team can be used during each match.
• A 10-minute time limit for each player will automatically be enforced in-game, beginning at the start of each battle. When a player’s time limit expires, that player will lose the game.
• At the beginning of each battle, players have 90 seconds to select one Pokémon with which to battle.
• At the beginning of each turn, players have 30 seconds to select a move or change the Pokémon in battle. If a player has not made their selections at the end of this period, the game will automatically make selections for the player.
• Players may battle up to 15 games per day of the competition. Any unplayed games will carry over to the following day. A new day begins at 00:00 UTC.

Source: https://3ds.pokemon-gl.com/information/683e22aa-5ebc-4a34-ae73-7472bc0938c9