On w2-3 they're is a maze of the moving wall things(idk what they're called) that has a piranha plant in the middle. Every 4 times the plant bites it stops for about a second. if you're on the left side of it when it stops biting you can run and fall beside it without dieing and keep going. If someone timed it perfectly in a run they could maybe save about 2 or 3 seconds at most. It probably wont help i just thought it was interesting.

It's pretty difficult but I've done it once or twice

I don't think I've seen that before, thanks for pointing it out.