Pokémon Diamond and Pearl/Lake Acuity

Lake Acuity (エイチこ) is home to Uxie, a Pokémon of the legendary trio.

Surf to its middle and enter Acuity cavern. If you have beaten Team Galactic at its headquarters and released Uxie, Mesprit and Azelf from the lab, Uxie will be waiting for you here. Save the game and start battle.

Uxie is easy to capture; weaken it, send out a Pokemon with much more leftover HP and start throwing Ultra or Dusk Balls. Try hard and you will get it.

Items

 * TM 14: Blizzard (requires Surf HM)