I played a mage and farmed goblins easily. Shamans were a little tough, but not really. I used magic missiles, the frost cone starter spell, poison starter spell, the net spell from the goblin archers, and the speed spell from goblins as well. I had over 1k gold and still hadn't finished all my goblin knowledge, I think just needed a few more shamans.

Shamans you could say were difficult, but if you are dying you should consider getting better at the game before calling it trash. All other goblins died so easily it wasn't a challenge at all.