I wanted to learn a 1-3 speedrun. I noticed a noclip in the beginning thru the glass above the double skull door in the current wr. I can't find any guides. I atempted to replicate it, and managed to see thru the wall but i cant figure out a way to clip thru it. Any ideas?

It's probably an arch clip. I actually had the same idea of trying to replicate it, but I couldn't pull it off. I'm not sure how comfortable you are with arch clipping, but I think you're better off doing it the conventional way of getting the blue skull as fast as possible and learning a hideous mass speedkill. Do you know how to speedrun 1-3 using the method I'm referring to? If not, look at a submitted speedrun somewhere lower on the leaderboards, as other than those two ways, I don't think there is much nuance in actually getting to the hideous mass.

Hope this helps!