When the topic creator mentioned Mario 2 I assumed he was talking about Lost Levels, did he mean the American Mario 2? That's not that hard, it just requires competent platforming skills.
Do self imposed handicap runs count?
I also wouldn't include any RPG where you can level up on a list of 'hardest games ever'.
And Contra's definitely a hard game, but once you figure it out, it's not so bad. I've beaten it on one continue without the code.
And Ninja Turtles 1 is only hard because of the glitchy jumping over fire with no headroom. That one jump in the airport is ridiculous but the rest of the game is fairly average.
1) Most coin op arcade games from the 80s
Every one was designed to murder you hard.
2) Battletoads
That effing surfing part.
3) Super Mario Bros 2, by that I mean the Japanese one
It plays like a fan hack.
4) Ninja Gaiden 3
I don't know why so few people have played this when so many know about the first two. I just read on Wikipedia that the Japanese version had no continue limit and the password system. But I can usually not beat the third boss, and one time I made it to 7-3 when the game froze, and I haven't touched it since.
Personally I think it's awesome that they changed the game in the US version to make it harder. Usually it's the opposite, they tone down the difficulty hard when they bring it over here. Catherine making the pillow give you more lives, FF4 easy type, and that ridiculous TacticsOgre port where you can rewind your bad decisions.
5) Castlevania 1
This game has a lot of the dickish kind of difficulty with things coming at you timed exactly when you jump and coming at you from angles where you can't hit them.