I'm having some trouble defeating Mannimarco. I can't hit him! Spells travel straight through him as do weapons, as do fists. AFAIK that's all methods of killing ruled out. And there doesn't seem to be any in-game method of killing him other than the traditional way. Is my game bugged? Or haven't i looked hard enough?

Not sure, but my character just kill him off with 3 ~ 4 power attack. Very easy, don't know what's the in-game fuss about him.

I didn't have any problems with him either, must be some kind of bug.

Well, since you can't possibly hurt him, it has to be a bug. I specificaly remember killing him with my custom lightning spell.

Ya, it would seem that it is a bug related to an in-game cut scene and the "rib" cage which is supposed to raise trapping you with Mannimarco. In my game, the cage doesn't raise until after he's dead (killing him involves getting him to follow you into the underwater tunnels where he drowns, meh.) In all, a disappointing appearance and demise to my favourite unkillable demi-god baddy from Daggerfall. :(

Really? I just jumped him and hit him before the big melodramatic expository gloat... Then the game got stuck in a dialog error and I just stood around, un-crashed, protection spells expiring, but no dialog.

So I re-loaded, let the meglomaniac speak, and pummled him big time. While he tried his silly magic and tried to hit my 85+ AC with is little silver dagger...

Took about 30 seconds and he was flying backwards through the air dead...