Hidden Message
At the game mode screen, enter the Sound Boy mode, then Program Play. Set any sequence of music tracks to play. Start playing it in the Through or Repeat. While the music plays, the pig character will walk around. Sometimes it'll bow to you. Press A+Start when it does so to reveal a hidden message.
Resurrect
Locate an energy unit after one of your fighters is killed. Stand near the energy, press Select, and choose the dead character to receive the energy.
Hidden Message...