During today's Nintendo Direct, new details about Pokémon Ultra Sun and Ultra Moon were shown off. The newest titles in the series will include several preorder bonuses, new Z-Moves, and new Ultra Beasts.
As seen before, the games will have a renewed focus on two different forms of Necrozma, born from a fusion with either Solgaleo or Lunala. These new forms are referred to in the English version as "Dusk Mane Necrozma" and "Dawn Wings Necrozma," respectively. On top of this, two new Ultra Beasts were revealed: UB Burst, who is exclusive to Ultra Sun, and UB Assembly, who is exclusive to Ultra Moon. Also, if you purchase the games before January, you will have access to Lycanroc's new Z-Move, which leaked earlier today.
Source: Nintendo Direct