Item Abuse is a Super Mario World hack, created almost as a proof of concept of a very high level of difficulty in games. It was an open challenge to those liked challenge, and a showcase of a large number of interesting glitches and breaks.
YouTube user and SMW hacker Penangbenny is highly steeped in 'Kaizo hack culture': the concept of creating highly difficult and sadistic hacks of Super Mario World, for the "enjoyment" of the players. To simplify the principle a little bit, the harder and more clever the hack, the better it was.
So, Penangbenny, hardcore TASer and general breaker of games that he is, came out with Item Abuse. It was a collection of, at the time, the creme de la creme of glitches and abuses, the hardest of the difficult maneuvers. I'd say it was hard even for the TASers, but that would imply it's actually possible to complete without tools. Featured within are such gems as every imaginable permutation of shell-related jump, bouncing off of P-switches for midair, having to casually jump no more than exactly one pixel high, and absurd cape flight sections. One area fires you out of a cannon, and expects you to uphold that augmented cannon speed for the remainder of the level, something that has to be done by pressing a jump button on every frame. Even the intro screen had a death trap that was irresponsibly difficult to avoid.
To summarize it, consider this: each room of the game has a fresh new swatch of colour for the foreground and background, but you're really too preoccupied with trying not to die to notice. If you'd like to see this monster for yourself, here is the first in a series of videos of a German-language Let's Play of the game, wherein someone attempts a tool-assisted playthrough: knowing the game and very little German, I can vouch for everything but the pace of the video, but believe me when I say it would be longer, slower, and actually somewhat taxing to play it for yourself.
Most of the puzzles have since been 'broken', which in TAS slang roughly means 'solved or completed faster than normal by using an unintended method'. The resulting TASes are crazy fast and amazing to watch. Of course, it has also spawned a sequel, Item Abuse 2, with updated and more difficult challenges, as well as even imitators trying to cash in on the "super creative yet highly difficult" aspect of the title, like Glitch Abuse, Pit Abuse, and so on.
All in all, this is a game that is just another prime example of the infinite perversity of man.