There's a legend to this one. I haven't bothered to look it up, but the story goes that there's this Super Mario World champion in Japan who's friend challenged him to complete his hacked levels. These are fiendishly hard levels that require just as much luck as skill. A more reasonable name is Kaizo Mario but I find the YouTube poster's choice to be more accurate in describing the pain:

That's just the first level. There are close to a dozen more of these. And if that's not enough there's a sequel that begins with this masterwork:

What I love about this one is how it totally subverts the Mario conventions. Hidden blocks are a punishment instead of a reward and the mechanics of stage completion are used against the player. It's all at once an example of what to do and what not to do in the area of game design.