Kaizo Mario World 2, also known as Asshole Mario 2, is a hack created by T. Takemoto for his friend R. Kiba. It features extremely sadistic, unique and groundbreaking level design. This is also the hack that started it all, since the kaizo genre wasn't existent beforehand. The literal translation of "Kaizo Mario World" is "自作の改造マリオ（スーパーマリオワールド）を友人にプレイさせる", or in plain English, "Making my friend play through my Mario hack (Super Mario World)". Kaizo is a rough translation of the word "modify" or "change" in Japanese.
The difficulty of this hack took me by surprise. Probably because it's overshadowed by Kaizo 3, I have not heard it mentioned with the usual hard but beatable hacks like GPW, Storks, Riff World, etc.
I beat GPW and Riff World in July in no-tool first playthroughs, and am 10 exits into Storks. I beat Kaizo 2 yesterday in a no-tool first playthrough and found it significantly harder than any of those. I spent something like 17 hours on Pandemonium, 12 hours on Ultra Star, and 9.5 hours on Castlevania.
Most of the hack was just miserable. In large part, that is because it is CLEARLY designed for save state play. The moves have no flow. They are discrete tricks, each designed to be as punishingly tight as possible, because the intent is for you to save state after each one. Some moves, like the spinjump off the last rock in Pandemonium, seem jank and luck-based. When playing RTA, the levels become a soul-destroying grind. I can't even award this hack points for creativity, as the level design closely resembles Kaizo 1, only far tighter.
I am posting this review as a form of grieving for the many hours of my life that died playing this terrible game, but also as a warning to all future players. Know what you're getting into.
Guys, it's Kaizo Mario World. Who really cares about the floating munchers. I think this is more than notable enough to be an exception to the rule. Not to mention it wasn't even submitted by the creator.