How do I catch Arceus in this game?

Actually, Arceus is an event only Pok�mon, so you must use cheats to obtain him, since his event is over. The event gave you the Azure Flute, which you blow at Spear Pillar in order to awaken Arceus. I got my Arceus from my cousin's R4i, and it is at level 9 right now. He came at level 5. My brother got it the same way, only his is deleted and was level 26. I hope that I've helped. MaPoLe3591

There have been rumors of the Azure flute event returning but with generation 5, no, You may conside visiting the SuperCeats action replay forum where you still may request those cheats. If you do get a cheat then take it to the top of Spear Pillar and climb the stairs to Arceus, and batte it, it's at level 80 so Ultra balls are recomended. The recomended level for the battle is about 85 to 86.

DO THE TRIO IT WORKED FOR ME GET THE LAKE TRIO

To encounter it you must have beaten the Elite 4 and have the National Dex. Then you must have the Azure Flute and battle it at the top of the stairs that appear at the top of Mt. Coronet while using the Azure Flute.
To Capture it: I would recommend using a lot of ultra balls and moves that put it to sleep. Also if you have a fairly strong Pokemon that knows false swipe, use it to give the Arceus exactly one hp while sleeping.