I was watching Whatanator's video on no major skips% and on level 25 he does a skip on cosmic, I decided to try it on pech desert for some reason and slid down the wall instead of clipping through it but, I didn't die when I hit the death plane. I have not recorded it but if it's fairly common ill try to record it.

I managed to record it:

i didnt think that this was possible on peach desert, but it wont help much unless you can get around the end platform

already known/doesn't save time here, it only saves time in cosmic

and moon as well

yep that is what i thought