My DK had lots of spare skill points, so I leveled up the skeleton summoning doll from act 1 and gave it a crossbow and splitting arrows, then had it switch to power arrows when the shadow creatures were all dead (my hero was also an archer, so having both use splitting arrows was quite effective).
You can also enter the BF repeatedly to check the merchants for better equipment for your hero or holy water to make permanent potions. Since the goal of the game is to separate yourself from the DK, I would not worry too much about upgrades for him at this late point in the game.
