Bridge Glitch:

Throw a bone at the gold skull and press the reset game button in the menu while the bridge is still rising to cause the bridge to be there before the timer starts.

Bone Launch Glitch:

You can throw a bone and immediately left click to punch it which sends it very far in a straight line forwards (this can be used at the start of the run along with the bridge glitch to hit the gold skull from the entrance to the next room).

Throwing Yourself Glitch:

It is very inconsistent but if you look up, jump, move in any direction and spam e then sometimes you can pick yourself up which can be used to clip through walls by throwing yourself through them (this is used in the any% run to get to the overworld without having a heart).