Easter egg
For this, you will need a Four-Score adapter to allow four controllers to be controlled at once. When you beat a random hockey battle, when you win, press A + B + Start on Controller 3 during the victory sequence. This will repeat the animation sequence.
Sound test
At the title screen, after "Push Start" appears, press A, Up, B, A, Right, B, A, Down, B, A, Left and B. If done right, the soundtest should appear.