Nankoku Shirei!! Spy vs. Spy

To see the credits, first enter the sound test code and while in the sound test menu, press Right, A & B on the 2nd controller and select "Next" to see the credits.

While playing versus the computer. On controller 2, hold A & B and yell at the Famicom's 2nd controller microphone. If done right, the computer will freeze for a few seconds. If you freeze the opponent on top of a hazard, all his energy will be depleted!

Right before a level ends (regardless if you win or lose), before the results box appears, press and hold the A & B buttons on the 1st controller. If done right, instead of the results box, you'll get the sound test.