However, the campaign enforces the occasional PvP fight from episode 2.
More notably, 68 out of the 87 cards in the game require a PvP rank to unlock. And the unlocks start at PvP rank 5 and progress to rank 10 and beyond, meaning you can’t just power through a few fights and be done with multiplayer.
So, without fairly extensive PvPing, you’ll be limited to just 19 cards.
Lastly, you can’t buy card packs with the regular in-game currency (though you do get a basic pack for free every fourth hour). They are bought through the IAP currency, which IS gained at a very slow rate through single player content, but at an accelerated rate through PvP. So, even if you attain all necessary PvP ranks to unlock all cards, card acqusition will still be very slow unless you either pay real money, or keep grinding PvP.
Vocalist of Neverlast
Game Center/OpenFeint/Plus+/[insert arbitrary game network, online character or multiplayer account here]: Ayjona