Mr. Chris said: Beating E1M1 on Nightmare under 30 seconds on the XBLA version a couple of years ago.
Nightmare is awesome. I've only beat E1M1 on Xbox 360 for the achievement and more recently I've beat E1M1 both in 25 seconds and 100%. Not at the same time though. I don't think I've even played any other levels in NM but I'm gonna try both parring and doing 100% on the rest of the game soon. NM is the only challenging difficulty.
Kontra Kommando said: Beating Doom and Doom II on Ultra-Violence; never really tried on nightmare.
My completionist OCD doesn't allow me to play on Nightmare. I never feel like I'm getting 100% kills (thus, no 100% score... not that I always achieve that goal anyway hehe). Also, infinite respawning is a bitch. Maybe one day I'll try a nightmare run. =P
Avoozl said: I once tried fighting a cyberdemon with fists only and managed to succeed surprisingly. Yes I know it has been done before but it's still the best thing I ever tried to do.
Once I ran out ammo and had Berserk picked up previously. Having no better chance, I ran against the Cyber and managed to punch it. Once. That was fair enough. One can never be sure if this monster has about 14 hit points left to finish it properly.
For awhile I was speed running PSX Final Doom on UV on any of the three episodes. Proud to say that I can sometimes get through 9 to 11 or so maps without dying. It would be more if I took my time, but speed running with the PSX controller is fun.
I think a pretty boss achievement of mine would be to beat my own UAC Ultra 2 maps on Nightmare. MAP05 and MAP06 are destroying me, but I know there's a thin little ray of hope. It really could have used a plasma gun though I think.