Kaizo Mario World (改造マリオワールド Kaizō Mario Wārudo, "Hack Mario World") is a unofficial Mario hack game released for SNES,but it can also be downloaded on the PC.Unlike the Official Nintendo Games,this game is nearly impossible,play at your own risk.
Kaizo Mario World is a series of 3 hacked "Super Mario World" ROMS.Kaizo Mario is one of the hardest games in the world,since it breaks the rules of "Accepted" level designs,and the levels have extremely hard patterns and many traps (specially invisible blocks). Kaizo Mario World not only features insane levels,in the game,you only have 5 lives (Unless you hack it).The game is also known as "Asshole Mario",might be due to difficulty.
Kaizo Mario 2 and 3 (The process is complicated and you need a SNES emulator and a Super Mario World ROM (To patch): http://kaizomario.techyoshi.com/downloads.html
Links to play it online
Kaizo Mario 3: http://www.classicgames.me/kaizo-mario-world-3.html