This game, like ME3 Multiplayer, forces you to buy RNG packs to unlock items. Soooo much easier to do when you have infinite (well actually 999,999,999) coins/money to unlock all the cards, characters, and support!
Here are my easy instructions on how to hack the game using iFunbox:
1. Connect your iPad/iPhone to your laptop/computer.
2. Open iFunbox
3. In iFunbox, open the Injustice: Gods Among Us app folder
4. Navigate to the “Documents” folder
5. Delete your PlayerSave.bin file (you might want to save a copy of it first for backup)
6. Copy/paste the new PlayerSave.bin file you just downloaded into the same folder
7. Open your game and you will have over 900 billion credits/coins/money!
8. Spend like crazy and unlock everything.