If you have Rage on your 2handed warrior, just teleport Alexander in front of your warrior, or your warrior in front of him. With a decent weapon you can crit 250+ on him easily. Also use Snipe with sneak on Sebille, that should chunk down about 700hp on Alexander. You can kill him easily in 1~2 turns. And don't use Source spells during the fight or the worm will spawn earlier, then it's gonna be chaotic.
