Sudai
Stuff here
You know how if you're in your Up-B and you run into a wall, you will bounce off that wall with equal but opposite momentum? Basically, people are running into a tiny "wall" on the bottom of a level where there shouldn't be one (logically or visibly). This is most likely caused due to design error.
If you still don't get it, go into training on Yoshi's Island and Up-B at the wall of the stage bellow an edge. That's what's happening but on the flat underbelly of a stage where there's no reason for it to happen.
If you still don't get it, go into training on Yoshi's Island and Up-B at the wall of the stage bellow an edge. That's what's happening but on the flat underbelly of a stage where there's no reason for it to happen.