In a completed game created here on pokecommunity that I downloaded, called Pokemon Raptor EX, you can catch Arceus. Now this Arceus is different because it has all the elemental plates, and you cant do any damage unless you break all the plates, now the plates themselves have to be hit a couple of times before they break. So say you use blizzard, it'll damage all the plates EXCEPT for the Ice Plate because its the same type (the same goes the other plates). Arceus is also immune to a master ball, so you gotta use diferent ones.
Now I used up all the balls I had except for pokeballs and I had 99 so for hours and hours i sat on my laptop until I finally caught it in a pokeball.