what pokemon should i use for the ultra wormhole

"While in Pokémon Sun & Moon you could travel to one area of Ultra Space, Pokémon Ultra Sun & Ultra Moon has changed it up by allowing you to ride on Solgaleo or Lunala to fully explore various areas in Ultra Space. This unlocks after you have gone through the Ultra Wormhole to go to Ultra Megalopolis and allows for you to go to various different areas to find different Pokémon, including Legendary Pokémon!

When you first go to Ultra Space, you will fly on Lunala in Ultra Sun or Solgaleo in Ultra Moon, but you can change between the two at will in Ultra Megalopolis. The controls are also initially purely motion, but you can switch to the Circle Pad in GAME FREAK's building in Heahea City.

Flying through Ultra Space requires you to collect various orange orbs of energy. These will increase the speed of your Pokémon and allow it to travel further distances. The more you get the better, as their appearances are very frontloaded, being very rare as you progress. In addition to the wormholes, you will also see blue balls of electricity. If you hit these, then you will slow down and lose some energy. With smaller energy, you struggle to escape the gravity of the wormholes and eventually get dragged into the next one."

Serebii about Ultra Wormholes.

The Ultra Wormholes are a new mechanic in USUM that allows for easier shiny hunting and is the place where you can catch all the non-flagship Legendary Pokémon and Ultra beasts of your respective game. Basically the farther you go in the Ultra Wormholes, the higher your shiny chance is, maxing out at 5000 lightyears.

 

You'll also be able to catch Pokémon not normally available in Alola. Sadly, there are no 'Dex entries for them