Altered Beast/Secrets

Sega Genesis
Enter the following codes on the title screen. These will also work on the Wii Virtual Console and Switch Online versions of the Genesis game, as well as 3D Altered Beast on the Nintendo 3DS.

Famicom

 * Sound Test: Press and hold while pressing the Reset button on the console.  By doing this, you should see the words "FREE PLAY" on the title screen.  Now press and hold  to enter the sound test mode.
 * Stage Select: Press and hold while pressing the Reset button on the console.  By doing this, you should see the words "FREE PLAY" on the title screen.  Now press the  button once for each level you would like to skip.
 * Hard mode: After beating the game once, wait for 30 seconds on the "Asmik" logo and press to begin the game in hard mode.