Ultra Beasts are a collection of
Legendary Pokemon that are classified as such due to the fact that they come from an alternate dimension. During the Main Storyline, you will encounter a few Ultra Beast; however, you will won't be able to obtain any of them until after defeating
Ultra Necrozma. You will battle the
Ultra Recon Squad with their Ultra Beast,
Poipole, on a number of occasions, as well as a wild
Nihilego the first time you visit
Aether Paradise.
As the story unfolds, Lusamine and the
Aether Foundation will selfishly look to use
Cosmog (who is actually an Ultra Beast in its own right) to create an Ultra
Wormhole in hopes of defeating
Necrozma on their own to prevent it from stealing the light of Alola. After capturing Cosmog from Lillie, Lusamine will attempt to do that exact thing by opening an Ultra Wormhole. However, by doing so, more
Ultra Wormholes will appear across
The Alola Region, forcing the Kahunas of each island to deal with them.
After defeating
Ultra Necrozma, you will earn access to traveling into and through Ultra Space. Ultra Space has a number of
Wormholes found within it, ones that can sometimes lead to the majority of the
Ultra Beasts. Since they are found in Ultra Space, these given Ultra Beasts will start with a stat boost due to the energy from the Ultra
Wormhole. Ultra Beasts found through
Ultra Wormholes have no limits on how many times they can be found. All Ultra Beasts can now be found in their Shiny
Forms.