It seems that Zagan is a lot more difficult in DKS. For those who are really stuck killing Zagan I found a relatively easy way to do it. It still takes a bit of work though:
Watch your health bar closely and use the Battle Tower menu to move back and forth between your tower (for healing) and the battle with Zagan. The monsters will not heal while you teleport back to your tower, so when you teleport back to the battle, just continue where you left off. Make sure you knock off the spawning nests first, and save before you leave your tower each time.
