It seems like the "fake town skip" is the only real glitch used, how do you do it? I'm trying to crib from polecat's run, and it's not working too well for me :\

I doubt the original poster still cares about this information, but if anyone happens to find this page through Google, the key to do the skip seems to place the skull laser, get hit once and then dash at the very end of the invincibility window to get hit just as you are about to hit the side cloud/ground. If you get hit as the side cloud/ground is moving from right to left (aka toward Dandara), you should sometimes clip through.

This takes a while to get right and then you have to be ready to immediately dash toward the "moon shell", else you might get clipped back through the cloud again.

If you are trying to do this for the speedrun trophy (as I was), make sure you have at least 7 health and you back up your save as soon as you enter this area.

This much health will allow you to have 2 attempts at clipping before dying/resetting your health on the tent, since you need to lose 2 hearts to lose contact with the floor (5 health left) and each attempt to clip will take 2 more hearts (3 health left, then 1 health left). With 6 or less health, you only gonna have 1 attempt to clip before the next attempt kills you, which is very suboptimal.

You want to spend no more than 3 minutes to clip through. If you take too long, restore your backup save and continue trying. Following Polecats' video for the sub 30 should give you plenty of time to do some fuckups, just make sure you only activate the save tents that they do, because everything they do is done for a reason. I saved too much and too often and was forced to pointlessly fight the golem/heart boss which took a good chunk of speedrun time away.