In some of the very first relased copies of Revenge of Shinobi for the Genesis.
If you do the cart swap trick you will get Super Shinobi. How do you
know if you have one of those carts...Does Godzilla in your game has his shin
on ? If he does you have a 90% chance it might be.

And Super Shinobi is a much better if not slightly harder version of the game