Originally Posted by Shankopotamus
Can you unlock all of the decks by playing the game? I guess what I'm trying to ask is; what are the things that you HAVE to buy to unlock them?
The initial $4.99 IAP gives you access to 10 decks, multiplayer capability and a bunch of single-player content. By playing through the single-player campaign, the decks are unlocked sequentially. Playing with those unlocked decks in any mode will unlock additional single cards (that you can use to customize the deck) every time you win.
The expansion pack IAP gives you an additional 5 decks, unlocked in the same manner, and some more single-player levels. Play through the campaign, then play with the decks to unlock more cards.
You can also spend further IAP ($0.99 per deck) to fully unlock all the cards in that particular deck, but this is not necessary to get everything.
There is one more IAP, Deck Pack 1, which isn't on sale. It gives you two more decks, but no single-player levels come with them.