Cresselia: To capture Cresselia, you need to interact with the Fullmoon Island Meteorite. After catching Cresselia and completing the game's main storyline, you can capture Mesprit and Azelf. Upon encountering Cresselia, its level will always be 50, so you must save before encountering it.
Evolution items: Two meteorites are evolution items in Pokémon Pearl. Each meteorite can evolve a specific Pokémon. If you interact with the Icicle Mountain Meteorite with Magneton and the Iron Island Meteorite with Tangela, they will evolve into Magnezone and Tangrowth, respectively.