How to preform
On any custom level, make a row of normal blocks. Directly underneath them, put thin panel layers that can be jumped through, so that they are hugging the bottom. Use Drill Rush and aim it into the bottom, and when you are inside the blocks, attack it with moves such Mach Tornado, etc. This can also be done by Marth by using Dolphin Slash.
Shuttle loop glitch
To activate the shuttle loop glitch, use the above said stage, but instead of using a Drill Rush into the bottom, jump into it until the player's head is pushing against the bottom, and then use Meta Knight's Shuttle Loop. Doing so should make him go right through the floor, making this a useful sneak attack if the other person doesn't know the glitch.
As a side note, assuming this glitch is supposed to place the player's character inside the row of blocks, there is a much easier glitch. On a custom stage, select the techno/mechanical theme. Next, make a row of the white, cylindrical drum shapes horizontally. Above these, make a row of standard blocks from left to right ending about half way across the drums (or as long as the player wishes, allowing for additions.) At the end of the blocks, place a staircase joining the top of the blocks to the drums (assuming the player went left to right, the top of the staircase should be left, and the bottom, right). Now, if the player gets a run-up from the right of the drums, they should pass through the staircase without climbing up it and be on top of the drums under the blocks. Notes: this glitch was performed on one of Nintendo's "Stage of the day's" using Kirby. Yoshi is also able to perform this using the Egg Roll, but since the CPU achieved this, it is unsure whether he can actually run through it like Kirby can.
Place blocks in one of, but not limited to, the two following patterns.
An alternative to this can be done in any stage theme, and is similar to the first method.
When playing the stage, as if the block isn't there, try using nearly any character's Up+Special technique to jump onto the platform below the block. If successful, the player will jump through the above block and onto the platform. Another way to do this is by backflipping into the platform, but this is considerably more difficult. Key is to aim for the platform's corner as you try.