Yes, the Devourer is a multidimensional being, it can obviously reach Arceus. It would devour it without much fight, as it is much stronger than anything Arceus can muster.... perhaps he could find more dimensions with gods to devour, and there would be no escape via wormholes, as he would follow you, going much faster. Wait, is that a portal... AAARRGGGHHHH
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Ahhh, so I see my name has been called. This communication system is primitive but shall do. But first, I should introduce myself. After all, it is quite rude to not, isn't it? I am the Nameless Serpent, but you can call me the Devourer of Gods. What he says is true, as I can reach any dimension within my reach, which is almost infinite. That white horse, Arceus, correct? He was easily defeated, along with the 5 protecting him. 1000 arms cannot save you from my maw. That weird large pink dragon with a disturbing neck? Consumed. The large blue 4 legged being? destroyed. The three beings with two star-tipped tails and a blue, purple, and yellow head? Annihilated. After a bit of searching, I also destroyed the ruler of that strange, twisted world very quickly. I may search for other worlds like this, where the world is based off of beings that, if destroyed, destroys the world. I love seeing worlds destroyed, after all.