Ammochain on N! AoMs. That was an epic battle. I homing-phased over to the nuke BFG, and then slowly walked my fire over to the left-hand side with a S1F3P1 Nuclear Plasma rifle. I managed to wipe out nearly all the enemies without much damage at all.
However, even this on N! AoMs doesn't compare to my most insane run, in which I did the Mortuary on N! AoHu with Ammochain. I used roughly the same tactics as I did in the previous run, but without a nuke plasma, and I only got hit once, which was from a lucky Arachnotron which rezzed itself. I had thought that it's corpse was a Vile corpse, so I didn't destroy it.
Another story was from a Blademaster N! AoRA run, in which I managed to melee-kill everything before the 3-minute mark. I had the Necroarmor and a set of Agility Grav Gothic boots, along with a Bulk Ripper. While zerked, my attack and movement speeds were .17, and my melee damage was (7d6+15)*2, averaging to 39.5 damage, or ~232.35 damage per second, without Blademaster added into the mix. I just ran for the Nuke BFG, shredding everything that was in my way. After that, I dropped down for the bulk mod, and then went to the upper left for the power mod. The moment I killed the final enemy, the Angelic Armor spawned in the space next to me. After I grabbed that, I immediately homing-phased to the stairs and went down before enemies could respawn more.
The Mortuary on N! AoOC is ridiculous, since you only get 3 levels of buildup time, without special levels. I did it that time with a Malicious Blades build, since that way I could have the resistances that Malicious Blades grants, along with zerk from a lucky Hatred Skull.
When I did it on N! AoD, that was really crazy since not only did the enemies respawn insanely quickly, but then I couldn't see where they were shooting from. That time I also did it with Ammochain, and I used a ridiculous amount of cells to nuke everything with a pair of B3 BFGs, after I grabbed the nuke BFG.
Seriously though, I have completed the Mortuary, in Nightmare mode, on every challenge except Ao100 (obviously). Even on AoPc, but there I just nuked it after grabbing the nuke BFG.