Is anyone else running into the bug where saving the game doesn't save changes to your deck? I saved my game after setting my decks, and when I loaded the save, the decks had gone right back to what they were before. I found I was able to save the changes if I changed rooms after and then saved, but that seems to be a pretty big bug.
I played the last version 0.3.0, and I'm not sure if this has been fixed, but in my version, the level is saved while the exp between levels resets upon loading. Therefore, you need to level up the card to the next level without loading. The easiest way is if you level up the card to 1 exp during purchase, forging, or battle, then scroll back in time using the mouse wheel and acquire the card again (exp doesn't reset when scrolling back). In the case of purchase/forging, it's better to save and load before doing this. In the case of a battle, when you scroll back, you'll start the battle from the beginning and need to finish it in the same number of turns to get the same card. After leveling up the card to the next level, a 'hard' save occurs, and you can't scroll back in time. Although this is a bug, the fact that exp resets upon loading is also a bug, so exploiting this isn't shameful. Additionally, if Destroy cards lose their level upon use, they will regain it upon loading, which is also a bug.