To me this is kinda weird because Arceus can learn all sorts of attacks no matter it's types.
Used because of all those resistances and immunity to Toxic. Very hard to defeat and like most Arceus can be a pain to defeat after using a couple of Swords-dances. Arceus can carry many stalling moves like Recover, Cosmic-power, Toxic, Wil-o-wisp, and so much more. Definitely hard to counter.