The Cresselia watched helplessly as Darkrai plagued the world with never ending nightmares, cursing the oblivious humans and Pokemon to sleep forever. "You need to stop this!" She cried out in despair, her words drowned out nearly completely by the raging storm. The shiny legendary concentrated to her full ability, and she used Psychic, managing to knock her opposite out of the sky.
"Stop! This is madness!" Cresselia demanded, still weak. Darkrai smirked at her, and though he didn't continue spreading his terrible dreams, he wouldn't wake anyone.
She knew why Darkrai chose to do this at that moment. Cresselia sighed in defeat, and used Lunar Dance, waking everyone who had been asleep and healing every injury they sustained. She saved the world, and at the cost of her life, no one would remember what she had done for them, what she sacrificed.
"Dreamcatcher... Will be my new name." The shiny Cresselia said weakly, and sighed her last breath, dissolving into a small, silver jewel.