This thing should have 255 base in every single stat and it's ability should turn every Normal-type move into the typing of the Plate (or Z-Stone) it's holding AND gain x2 STAB instead of just x1.5. It's catch rate should be so low, that it cannot be captured with a Poké Ball or a Great Ball.

I mean, Arceus is not supposed to be usable in tournaments or in-game battle facilities, so it might as well be THE definitive Pokémon in terms of attack and defense. As it is, it's kind of underwhelming.