Here's how to do it:This must be done on the final castle of world 4.
You need at least 2 players to do it and one of them must have ice power.
At the spot in the video where the fence has a long rectangular switch panel, kill all the koopas but one.
Have one player get on the switch panel and wait until the koopa is also on it.
The player on the panel hits the switch causing the panel to flip with the koopa on it.
While is it flipping, the other player freezes the koopa. You have to freeze him while he is on the switch panel and while it is moving. If you do it correctly you'll get the result seen in the video.