Essentially, you want to block someones attack with your turtle shield so they bounce backwards and fall off the platform. You press
to raise the shield and the opponent will bounce backwards if they attack you from the front.
Obviously doing this with the enemies back to the edge is easier than having your back to the edge and them traveling across the entire platform to fall off the opposite side.
This can be done locally with a second controller, which is much easier to coordinate. Feel free to slow down the map speed if you need more time to set up the controllers.