What deck do you hate more than anything? It can be in PvP or an AI's deck.
For me, speedbows are the worst. I won't post a deck code because there are many possible variations, but they are so similar and so prevalent in PvP, it's almost as if clicking the PvP2 button is clicking a "let's see how my deck performs against speedbows" button. It's a major reason I don't play Elements anymore.