Sound Test - At the title screen, press and hold Up, A & B on the 2nd controller. If done right, the sound test should appear.

Stage Select + Invincibility - At the title screen, press and hold Up, A & B on the 1st controller and Down, A & B on the 2nd controller at the same time. If done right, the stage select menu should appear on top. Select levels by pressing the B button and press Select to turn on the "TEST" mode which gives you invincibility.

Level 2 - 3196

Level 3 - 3569

Level 4 - 1719