Sacred Haven of Debauchery

Well, I spent an hour and a half fighting this dragon lich, I was so tired =\ almost nothing affects it, even fire doesn't always work. I used spells on it, scrolls, got rid of the staff, and used several potions (with various liquids), but I killed it.
In the screenshot, you can see the dragon lich and my summoned dragon (I finally leveled up the wizard and learned the spell).