If you enter a level and change the gravity immediately it can cause weird things like this to happen with the enemies. I've experimented with this on other levels and so far this only happens on the regular enemies that just go back and forth. What I think is happening is that these enemies bug out and for some reason change gravity when only the shooting enemies should be able to do that. Then they might land somewhere and keep their velocity causing them to move through walls. Sometimes an enemy will disappear but I think it's falling off the screen when that happens

As a speedrun strat this can save time as a way to move enemies so you don't have to shoot them. Overall I think this would save like 10 seconds if you do this on every level that saves time. I think this is a first frame trick, but it might be like the first few frames since I can get this kind of often. It may also be a glitch where it's because it's before the enemy has rendered, meaning it's probably a few frames window. Not worth to do this right now if it makes the level harder, but I'm starting to go for it in some levels where you can't get punished by doing it and it doesn't change the route

I've found another glitch where there are some places in the ceiling and floor where you can fall into and not die, but I don't think it can save time you just get trapped