Floor glitch
The Floor glitch is a glitch that requires Meta Knight on a custom stage. On any custom level, make a row of normal blocks. Directly underneath them, put thin panel layers that you can jump through, so that they are hugging the bottom. Use Drill Rush and aim it into the bottom, when you are inside the wall/floor, attack it with moves such Mach Tornado, etc. This can also be done by Marth by using his up b.
An extension of the floor glitch is the shuttle loop glitch, in which you use a Shuttle Loop to go through the floor. When you are underneath the floor, jump up till your head is touching the bottom of the floor. Immediately do a shuttle loop, and you should go through the floor. Doing this will sometimes teleport you a small distance horizontally. It is not yet known how to control this.