Several issues
You buy cards in this game but only four are available at a time and you don’t get to choose which ones so you could go into battle with the worst possible cards. I have found no way to regain health except to play healing cards during a battle so you might have to go into battle with very low health against tough monsters and have to hope you have healing or shield cards available. And playing those cards can give the monsters cute chance to summon more enemies or grow stronger. This is such a huge disadvantage that I lost interest on the game.