Video: In mid-2015, an intrepid modder called Obitus1 released one of the hardest Super Mario Bros. 3 hacks ever. Now, watch speedrunner mitchflowerpower absolutely kill it. Named Kaizo Mario Bros. 3. in honour of the infamous Kaizo Mario World series, this set of 19 levels is filled with near-impossible jumps, devious tricks, and items that you have to use in some truly unique ways. (Did you know, for example, that if you run off a ledge with a Kuribo's Shoe, you can get a free jump?)
Unlike most Kaizo-style levels made in Super Mario Maker and elsewhere, this hack is based on Super Mario Bros. 3, not Super Mario World. SMB3 can be way tougher, with more slippery jumps and far less forgiving mechanics.
The whole AGDQ run, which you can watch above, is really worth your time. Mr mitchflowerpower does some incredible things.