You can now sign up to battle with Pokémon from the Johto and Alola regions in the upcoming Johto x Alola Online Competition! This competition will be the first where Trainers will use the new Pokémon Ultra Sun and Pokémon Ultra Moon games. Registration is open until Thursday, December 14, at 23:59 UTC. The competition goes from Friday, December 15, at 00:00 UTC, until Sunday, December 17, 2017, at 23:59 UTC. Trainers will be limited to 15 battles per day. Junior Division players (born in 2003 or later) are limited to playing between 6 a.m. and 11 p.m., based on the easternmost time zone in each player’s country.
You’ll need a Pokémon Trainer Club account. After you log in, you’ll be able to read and accept the regulations on the PGL. You’ll also need your own Pokémon Ultra Sun or Pokémon Ultra Moon video game and a Battle Team of eligible Pokémon. Accept the regulations on the Pokémon Global Link by Thursday, December 14, at 23:59 UTC, and get ready to battle! All qualified participants in the Johto x Alola Online Competition will receive 50 Battle Points. Players must complete at least one battle to qualify.
Source: Pokémon Global Link