Just wanted to mention a couple of things I learned. On the last battle most people get killed. It seems to be the hardest one. If you are a Wizzard it helps to hide under the stairs and use burning hands on everything. For some reason they cant seem to get you there. Some kind of bug in the system. The other good place is at the top of the stairs. This works if you have a level 4 group. Hope this helps.
One more hint. You can make any one thing your pet in catacombs with the Command Undead Spell.
I personally found Invisibility, Undead Spell and Burning hands very useful here