Several Legendary Pokémon are available in Brilliant Diamond and Shining Pearl, with most able to be obtained in just one version of the game.
One of these, Cresselia, is not like typical Legendary Pokémon in that it's not found in Ramanas Park.
How to Unlock Cresselia
Once you've beaten Cynthia and become Champion, you'll need to register all 150 Pokémon in the Sinnoh region.
Then, return to Professor Rowan in Sandgem Town, and he'll upgrade you to the National Pokédex.
Head to Canalave City, and enter Sailor Eldritch's house south of the Pokémon Center. Speak to his wife and son, then go outside and speak to the Sailor himself. He's on the pier.
Sailor Eldritch will ask if you want to go to Fullmoon Island. Naturally you should say yes.
There's not much to do on the island except follow the path.
You'll come to a cave, where Cresselia awaits. Interact with it to trigger its escape.
Pick up the Lunar Feather and return to Canalave City.
Now that you have the Lunar Feather, take the opportunity to wake up Sailor Eldritch's son.
Now we can hunt Cresselia.
Just like Mesprit, Cresselia is a Roaming Pokémon, and can be found in different areas of Sinnoh.
Make sure you have the Marking Map app for your Pokétch (from the Pokétch Company President in Jubilife City) and start to visit areas where wild Pokémon spawn.
When Cresselia is pinged, immediately use Repels so that you don't encounter other wild Pokémon - this will cause Cresselia to flee.
Save your game, and approach Cresselia to engage.
Moves that prevent fleeing, such as Mean Look, will be very useful here.
Meet Cresselia, the Lunar Pokémon
Capturing Cresselia can be challenging. Here's what you need to know about the Lunar Pokémon.
Like all other Legendaries, Cresselia is susceptible to attacks that cause Paralyze or Sleep.
Additionally, try using a Quick Ball at the start of the battle, and Timer Ball if the battle goes on more than ten rounds -- however, it'll likely flee by then.
As mentioned previously, moves that prevent fleeing, such as Mean Look (learned by the Zubat and Gastly families, for example), will be key to catching Cresselia.
False Swipe is also ideal for lowering its health so that you don't accidentally knock it out. It will not reappear if it faints, which is why you absolutely must remember to save before the encounter.
Shiny Cresselia
Cresselia's shiny form is relatively easy to distinguish.
