Asked in Pokemon Diamond Pearl and Platinum
How do you find mesprit in Pokemon Pearl?
After you defeat the Pokemon League (Elite Four and Champion) go to Verity lake, the one closest to your home town. Once there, surf into the middle of the lake and enter the small island in the middle. Talk to Mesprit, it will show the Pokedex entry picture of it in the middle of the screen, then Mesprit will flash (disappear and appear) several times before banishing. If you don't already have the Poketch app "Marking Map" get it. A little face appears where Mesprit is. Track it down to that area, and you can find it like a normal wild Pokemon(in grass, on water, etc). After one move it flees the battle, but you can still track it down using the "Marking Map" app. If you want to keep Mesprit in the battle, get a Pokemon whose ability is Arena Trap (Dugtrio, Diglett, Trapinch), or have a Pokemon that knows Mean Look(Stops the Pokemon from escaping).