When you get to the dead bog level which is early in the game after you ride the horse to get away from the lycanthropes. You'll come to a drop of point where you can't go back in the level after you drop off. You'll enter a Goblin camp where Goblins will respawn indefinitely as long as you don't throw two grenades from a goblin that either throws one at you and misses or you grab the Goblin and perform the sequence of knocking the Grenades from the Goblins' hands. It's O.K. to throw one Grenade at the tree but no matter what don't throw two at the tree or the Goblins will stop respawning indefinitely. Just keep killing the Goblins for easy Experience , You only get 5 experience points from each kill so it will take a while to get all the unlockables but patience is a virtue.