The game is not soo much about what level you are at, the cards you have and are using are much more important, and for the most part there is no use trying to level up until near the end of the game because you are just wasting time when you can be leveling with better experience near the end. If you ever have trouble beating a boss just arrange your cards according to the weakness, and if you dont have many cards and its really hard then I guess you could find enemies that drop the cards you want and fight them, but leveling does not matter as much. The only boss I had to fight quite a few times was pretty far on near the end(Im assuming near the end at least, havent beat it yet but just finished my biggest semester project so hopefully I will have the time to finish it now). Great game, don't try to get all of the cards like I was doing because you will feel really bad when you find out you miss one.