I've been starting to speedrun this game and I am blown away on how the level dupe glitch works. I've started speedrunning the game but I can only do the noclip glitch, and not the level dupe glitch. I would like to learn how to do it so I could get better times.

EDIT: I've found a forum post on how to do the glitch, and now the only thing that I think I need is a level to import. If someone has a working level, putting it in here would be nice, but if not you can tell me what to add so that it would work. I'll update this forum if necessary.