(Sorry for my english, I'm not a native english speker !)
Excellent game ! I love trying to achieve the best time possible and finding tricks to go faster =) !
I found a very interesting glitch (speedrunly speaking) that allows you to "clone" your hero, and even if I don't want it to be patched (it is so fun and I'm sure it can lead to insane times), I have to tell you :
if you retry at the same time than your death (may be frame perfect, but I'm really not sure. It is quite difficult to do), the death sound is played twice and you now control 2 heroes, one over the other. You take double damage while your heroes are superposed, but if you die, only one will be teleported to the save point and so you'll be able to really control both. Unfortunatly, the camera follows only one hero and, if you want the "shift" button to work, you must have an odd number of heroes (but you take even more damage). The enemies will detect only one hero, ignoring the other.
I am currently enjoying playing with that glitch, trying to use this to beat the game in the fastest possible way (one hero goes for the walljump upgrade while the other is on the way to the double jump, for exemple) and would be sad if it was fixed =( xD !