My approach:
May not be a big help to you!
As a survivor, went into stealth as soon as I entered. Tried hellspikes from stealth. Nevertheless, the Lord of Lies generated innumerable troublesome foes that attacked PC.
Once this happened, focused all my efforts on Lord of Lies, gobbling down restoration potions (I had 31 on entry, finished with less than 15). This brute force approach did win (though it took me about 4 reloads to do it!)
