I think Doom's nightmare mode was the complete opposite of artificial difficulty, it required you to know absolutely everything about the game, right down to the spawns of enemies, how to move, where to move and where the health/armor powerups are.

I was more talking about boss battles where one missed step was insta death, i agree with you on some permadeath though, i fucking hate it.

And yeah Four kings can fuck off haha, that being said the actual game Dark Souls+Demon Souls isn't something i'd put in that category i was more talking about 2-3.