Ok here's what you do. Make sure you have ice. Go to the last castle in World 4. It's difficult to describe exactly, but find the spot close to the beginning where a Koopa is going around a square of fence, which is flippable. Get the person with ice to jump on the closest of the two ? blocks beside the fence. The person on the gate should be on the BACK of the gate.
Timing is essential. Work out the timing together and get the person with ice to shoot a snowball, freeze the Koopa, and as soon as you see the Koopa frozen in Ice, flip the gate.
The product? Find out for yourself. And whatever happens, DON'T RUN AWAY FROM THE ICE BLOCK. It will make the frame rate drop dramatically. To exit the level, get everyone to press "A".