Step 1: Don't send your whole party in through the front gate, it's a death trap!
Send one guy in, hugging the left wall(this will prevent the mage from nuking you on the first turn) and start the battle with Alexander. At your first chance, teleport your dude out back to behind the gates and prepare to meet alexandar. I'd suggest just teleporting him away every time he gets close to the door, so you can focus on the gheist, the knight and the rogue. Once the worm comes and Alexandar begins fighting it, the rest should be a cakewalk.
If you send only one guy to attract the aggro, you avoid both the rain of death unleashed by the mage as well as Alexandars blinding radiance. Also, remember to use bless on the target that needs it the most! It can really protect against many effects.
This is actually one of the fights that I found alot easier playing with just one character, as it is much easier to avoid enemies and dance around them when you only have to keep one character safe.
Last edited by Storsorgen; 22/09/16 01:59 PM.