completely dominated every single challenge using the black deck, i probably only lost twice, and that's because i couldn't pick up a creature card for six turns X_X
well, dude1819, you really don't beat the baron. All you need to do is keep the guy with the sword alive, since he does 1,000's of damage. Eventually he will kill the baron.
it all depends what level you are playing. You have to reset your skills every level according to what kind it is. If it has all fire reistant enemies, you won't want fire. And for marathons i normally unluck one of the advanced units since i get so much cash.
The big thing is change to what level you are on, no one unit is completely dominant in this game.