Dude, Macheap vs Arceus is Macheap vs SPs. If they get enough out before you can do much, then you lose. I beat KingChamp with Arceus at worlds because I kept Macheap off the field. Sure, they got out, but not enough to win. Arceus vs Dialga means you go agro-Arceus and use the Lv.X to pump yourself up and hit Garchomps for weakness. It's just a really fun match when both players know what they're doing.
lol Froslass for Donphan.
~L_X_F