I have a Shiny Arceus in Heart Gold, and yeah, I know the only way of getting it is using an AR, (at least that I know of...) so I was messing around and I noticed that the Shiny Arceus is a hell of a lot better than the Event one. It's max HP is 444, while the Event one's is 363. It's stats are also a great deal higher than the Event one and instead of it's ability being Multitype, it has Wonder Guard, with makes most attacks do nothing. It also comes with an Exp. Share instead of a Rowap Berry. I know shiny Pokemon are supposed to have better stats than the non-shiny ones, but I didn't think this much better. If it turns out to be normal, then I fell kind of stupid for making this then lol.
It's not stronger simply because it is shiny. Only in GSC were the shiny Pokemon "stronger" because their shiny factor was determined by their individual values, often above average stats. In recent games, the shiny factor is determined separate from a Pokemon's stats.
444 is indeed the highest possible HP value for Arceus, but a normal Arceus could be that strong too. It's possible to legitimately obtain maximum IVs (31) by abusing the game's pseudo-random generation. Then, one can raise its Effort Values in the HP stat. It's impossible to go beyond the total EV limit of 510, though. So, legitimately, at most it would have two maximum stats. I suspect that since your Arceus has Wonder Guard and is illegally shiny anyways, someone edited it to have the maximum stats everywhere.
Note that you can't offer it in the trading section here. There's not much to discuss, so I'll go ahead and close this.