¤¤¤PLEASE BE AWARE¤¤¤ Most of these glitches only work on the Steam version of the game. The 3DS and Wii U versions were done in another game engine and came out almost a year later than the steam version. It's pretty glitch free.
Intro Stage text skip
On the 2nd to last block of the stage, right before triggering the end of level transition, pause the level and exit the stage. If done at the right location, you can skip the end of level text and proceed onward to the level select stage. If you do it too early you will go to the title screen. This trick is important because not only does it save 2 seconds on this level, but it also skips the boss text for the blizzard of balls stage saving an additional 7 seconds. I'm not sure why they are related, but they are and I'm okay with it
Mike Glitch: When you have only Nerd and Guitar Guy in the party, you can mash the “<” button and the Attack button at the same time, to use mike’s saber. This allows you to break down walls without the use of mike.
Zip Glitch: Although useless in an Easy Speedrun, it could be useful for a YOLO% Run.
Falling Death Glitch: When you die while falling, you body will continue to fall until it hits a platform or goes off screen. This means you can die and hit a previous checkpoint to get sent backwards in the level. This mainly occurs in Future Fuckballs and Happy Candy Fun Time.
Jump Glitch: By jumping at the same time you change characters, the first characters jump height will be transferred to the new character. For example, if you are mike then jump and switch at the same time to guitar guy, Guitar guy will then jump as high as mike can! This can also be used to reach some otherwise unreachable locations. Using Mike and BS Guy's double jump you can get a super high jump.
Checkpoint corruptions: This is a pretty major glitch that we don't completely understand quite yet, but I'll try to explain it as best as I can.
To start off, checkpoint corruptions are basically us doing something to make the checkpoints spawn you in weird locations. Normally you would simply return to the checkpoint when you die, but now we can respawn at strange locations, some locations could softlock the level permanently. Leaving and re-entering a level does not fix it.
There are two ways to trigger a checkpoint corruption that we know of. Both involve recruiting characters. You can either die while the character is talking to you (before entering the party) Or you can exit the level while he';s talking to you (again before he enters the level)
So far this is only possible on Future Fuckballs and Beat it and Eat it. I suspect it could be possible on Dungeons and Dickholes as well, but I have yet to get it to work through any known methods.