As ernie said mostly what cards you need are based on what Bakugan you play with. But there are a few exeptions, like “Call of the Defenders”, which gets all the bakugan you lost in battle back, “Magnetic acton” or “Attractor”, which move your opponents' Bakugan to your Gate card, giving you a homefield advantage, and a couple others I can't seem to remember at the moment. One thing for sure is if you do decide to occasionally brawl, your cards are your offensive and defensive, make them count.