Cresselia soared around Fullmoon Island and used Lunar Dance, which healed all the Pokémon that suffered nightmares on the island. Palmer obtained a Lunar Wing that saved Eldritch's son, and Palmer obtained Cresselia, too.
Palmer sent Cresselia for himself and Platinum to fly off from the Battle Frontier. The two flew off, while Mira, Riley and Cheryl were sailing on the boat. While they were riding, Platinum asked Palmer about Cresselia, and he told her about the story how he encountered it. Soon, the machine took them to the Spring Path, which led them to the Sendoff Spring.
As Darkrai was going to use Hypnosis, Palmer sent Cresselia, who fell asleep from the move. However, this was all so Cresselia could use Psycho Shift, which transferred the status to Darkrai, making it fall asleep. As Darkrai recovered, it continued its battle with Cresselia. When Charon attempted to escape, Palmer gave his Cresselia to Platinum, so she could follow Charon.
Once Charon was arrested, Palmer and the rest came out of the Distortion World. He decided to keep Cresselia for himself.