Sidescrollers are called as such because the screen scrolls from one side to the other and you go from left to right, often beating up bad guys, sometimes jumping on and over platforms and more often than not dying a lot along the way. Some of gamings most classic titles used this principle, but what if you flipped them on their head?
That's what one hack has achieved with the original Metroid game, twisting it so that instead of a horizontal side scroller, it's a vertically scrolling one instead. This makes the game far harder and some are now trying to beat it - with mixed results.
Of course there's lots of jumping involved, often off-of walls and in some cases you need to perform an intense number of bomb jumps in short succession. Surprisingly the game does work though. It certainly plays differently than the original game, but Metroid is a great choice for this type of experience since it already involved a lot of jumping - and Samus is rather well equipped for that sort of endeavour.
Learning the level layouts will probably be a requirement to finish this one though, as some areas have you dropping down on enemies that you cannot know exist until you reach them.
If you would like to have a go at this fiendishly difficult looking experience, you can download the modified game for free here.