This glitch is done in Wendy's Castle. By freezing a fence climbing Koopa and then flipping the gate at good timing you get infinite coins. However it causes the game to lag a lot and possibly freeze if there are too many coins on the screen.

Once again an ultra shortcut was found, this time in Wario Gold Mine. It was originally discovered using mods but someone found a way to do it without! This is not me, this is a world record I filmed on my Camera.