How to Unlock Cresselia
Like the other Legendary Pokémon in the game, Cresselia isn’t an easy find. In fact, catching this Pokémon requires you to have completed the main story.
Once you’ve done that, you can speak to Volo. Volo is the Ginkgo Guild Merchant you’re already familiar with, as you’ve crossed paths numerous times in the region. He’ll take you to Cogita, and you’ll receive Mission 23: The Plate of Moonview Arena.
Once you’ve got this mission, head over to the Coronet Highlands. Once there, go to the campsite near the Sacred Plaza and walk west to Moonview Arena, as the request name suggests. You’ll trigger a cut scene with Melli, who will take you to the arena where Cresselia is waiting to do battle.
How to Get to Cresselia
This Pokémon is a little tricky at first. It has a psychic forcefield up which reverses your controls — as you start to walk towards it, you’ll realize you’re walking backwards!
To get past this, hold the joystick all the way down the moment you enter the arena to walk directly towards Cresselia and throw a Poké Ball. It’s too early in the fight to catch the Pokémon, but this will break through the forcefield and allow you to launch a Pokémon to do battle.
Cresselia will be Level 70 which makes this a pretty challenging fight. The battle, however, is the same as any other once you get past the forcefield and doesn’t require you to whittle down health by throwing and dodging anything (like Arceus and the Frenzied Pokémon do).
As Cresselia is a Psychic-type, Ghost, Dark, and Bug-type moves are going to be your biggest asset in defeating Cresselia. Make sure to use Strong and Agility Attacks wisely, and don’t send out any Fighting or Poison-types, as that’s a sure way to lose the battle quickly.
The Legendaries are set up to be pretty hard battles but if you’ve gotten this far in the game, your Pokémon shouldn’t be too far off Cresselia’s level. The good news is it’s six against one, so you should whittle down its health quickly.
Be careful. As with any other Pokémon you might come across, you don’t want to deplete Cresselia’s health all the way so hold back a bit if you have higher-level Pokémon going up against it.
Whittle it down to yellow or red on the HP bar and then begin to throw balls. Ultra Balls are the best things to use in this scenario. Great Balls may not cut it, and Poké Balls have basically no chance.
If you’re stocked up on balls and can keep throwing them once Cresselia’s health is down, you should be able to catch it and add it to your team or pastures.