So you have been wondering how the heck do you get What's Updoor clip since Hakita updated the game. This is the most painful clip and I'm not lying about how this took me an hour. It's pure pain let me give you that, and secondly you're going to want to start off in 0-2 The Meatgrinder. Now before you spawn in any enemies, the glitch does not require any enemy spawns meaning it is easy for a pacifist run, but pain for the glitch in general. Walk through the level and stop here:Literally the second room in the entire level it's so easy to do this thing called "walking". Next, you're going to want to get out your rocket launcher and face this way, which when you walk in is the right side NOT THE LEFT SIDE (no enemy spawns needed).
Next thing you want to do is slide and then rocket UNDER yourself as you slide, do this repeatedly if you didn't end up on the top pipe.
Now face toward the other pipe and then do the same thing. Slide then rocket UNDER yourself. If you do that correctly you should end up here. And I did repeat this above 20+ times because it is so hard.
You're welcome for showing you this, I hope you have less pain than I did because I did this 20+ times and it was pain. The trick is you have to slide far enough to be under the opening but not under the upside-down ramp. Then you have to rocket boost upward shooting from UNDER yourself. Good luck on the clip (No, seriously it is the hardest one)!