Marriland plays through the American version of Pokemon Diamond. This is part seventy-four in a continuing series.
In this episode, Devin goes off to catch Uxie, the Being of Knowledge, in Lake Acuity.
If you're having difficulty catching Uxie, try teaching one of your Pokemon False Swipe (can be purchased at Veilstone City) and using that to bring Uxie's HP down to 1. Paralyzing and putting it to Sleep are also very effective ways to make it easier to catch if you have Pokemon with such moves.
It's probably best to avoid using your Master Ball against it, since Mesprit and Cresselia are harder to catch (and Cresselia is a lot more useful).
You can also find an overwhelming amount of information on Pokemon Diamond and Pearl at my website:
It has a full Pokedex and complete Walkthrough so you'll know everything there is to know!
EDIT: The man in green in the Poke Mart is holding the Manaphy I got from the Manaphy event.