You must get the Lunar Wing from the Strange House that’s located outside from Reversal Mountain. With the Lunar Wing, go to the Marvelous Bridge and Cresselia will appear. Save your game before you interact. Cresselia is on Level 68. If its HP is low, it can sometimes use Moonlight so make sure you have a Pokémon that knows Taunt or Heal Block. Wait till night and use Dusk Balls for better capture results. If Cresselia reaches Level 84, it will learn its signature move Lunar Dance, a move that makes the user faint and heal the next sent out Pokémon.<br />...<br /><a href="https://www.youtube.com/watch?v=iLhnmfhOY_U" target="_blank" rel="nofollow">https://www.youtube.com/watch?v=iLhnmfhOY_U</a>