The dark knight victory was x4 believe it or not. I don't think this dungeon generates nearly as many monsters than a playthrough of GC though.
The only other 'victory' is x2; see if you can discover it.
Necrodude isn't really looking for the sword, but I agree the message is weird. His dialogue needs to be rewritten, he's basically speaking ad lib right now. Talk to the master guard in XT1 and he might give some hints.
Assuming you don't mean the previously existing chaos ending, I've used wizard mode to try the following so far:
* Talking to the master tomb guard while holding the sword and the skull of Xinroch and being Infuscor's champion
* Zapping wands of resurrection and necromancy on the skull of Xinroch
* Haven't resurrected or neck-romanced Xinroch's corpse because he doesn't leave one
* Talking to Petrus with the sword
* Sacrificing the skull and sword to Valpurus and Infuscor while being Infuscor's champion
* Spawning the resurrected Xinroch in XT1 (to simulate leading him back through the portal and up the stairs, if that's even possible). He's on the monster team, so the tomb guards attack him. It was quite a balanced battle compared to Attnam - give it a try!
* Talking to the resurrected Xinroch while wearing the shadow veil and being Infuscor's champion
* Using a lyre of charm on him with 101 charisma
* Cloning him (he doesn't get cloned and there's no message)
* Killing the master tomb guard and talking to Petrus and the prisoner while carrying his corpse
* Sitting on Infuscor's altar after killing the master tomb guard while Infuscor's champion
It seems to be a well hidden x2 victory
* Putting the skull and sword in the coffin in the cellar (which sometimes crashes the game)
* Talking to
I'm interested to see what happens if you disarm Xinroch, leave him alive, and go back to the surface with the sword. That seems like a bit more effort to set up, though. And not likely to be a x2 victory.