Zamboni in introduction sequence:
Hold R + L and power on the Game Boy Advance. Hold the buttons until the Zamboni appears instead of the puck during the introduction sequence.

Bonus teams and extra creation points:
Wait for demo mode to begin, then hold Select and rapidly tap L, R repeatedly. When the demonstration is about to end press Start but keep Select held while tapping L and R. Keep tapping them until you hear a voice say "It's in the game". If done correctly, then you should get the Budcat and Tiburon teams in exhibition mode and 1000 points for creating a player.