I've tried playing this a bit. Pretty dang insane. Made it to the "tetris" room a few times, but could never get past that.
I'll have to look into I Wanna Be the Guy: Gaiden at some point (maybe also I Wanna Be the Fangame, or whatever the fangame spinoff was called)
I saw a TAS of this game (the original) once, pretty insane. A prominent glitch used was if you managed to stand on two falling platforms at once, when you land (or was it when those landed on you?), you will start to zip in some crazy fashion, allowing them to skip whole rooms easily, and in one case, get to a glitched "room change border" allowing them to skip a decent chunk of one of the three paths.
Oh yea, and the "spawn where you where when you hit the save" mechanic was abused quite a bit too, including a trick where if you did it right in some cases, the room wasn't completely reset to the state it was at when you hit the save, allowing you to repeatedly die, reload, and slowly "eek" through the room even though you are continuously reloading.