Back when my buddies and I played Neversoft's classic Tony Hawk's Pro Skater 2 on Dreamcast all day, we had the Start-scroll-A button motion down to a science--it would open the pause menu, and select the reset option. In our quest to perfect our scores, we had it down so fast you really couldn't see it happen with human eyes.
Playing I Wanna Be the Guy: The Movie: The Game, a brutal PC tribute to classic platforming crafted by Kayin Nasaki, brings back that feeling. The difference is that in Tony 2, I was trying to make my tricks better, whereas in IWBTG--a game in which you die with a single hit--I am simply trying to get through each devastating screen alive.
The game's official site has some context for the project and some instructions and tips that are worth reading, but if you want to try it yourself I would highly recommend heading over to FileShack, because the official mirrors aren't so hot.
Please note: this game is hard as hell. It is fucking hard. It is made slightly more manageable (though I don't think I would say "easier," per se) by having a working knowledge of classic video game platforming--it will cut down on the trial and error.
After you've gotten your ass sufficiently kicked, go check out this impressive video, which sees a player reach nearly seven minutes before dying or using a save point. If you're absolutely stumped, check out this full game map (you might want to click the "full size" link). IWBTG actually has a somewhat Metroid-esque nonlinear structure, adding a layer of complexity to the already unforgiving affair.
(Call bullshit on IWBTG's insane challenge? Think it's too cheap? Think the level design is more unfair than clever? The author defends himself on his FAQ page:
"I...come up with something new and surprising on basically every screen. Half the screens have unique events and situations programmed expressly for them. Each level has to be play tested over and over again to find a balance in difficulty and avoid easy exploits. I must keep the game difficult, but balanced. I must keep the player on their toes and yet still have to surprise them when they're most alert.")
Just watching that video gave me hypertension.