Penguin Wars

Penguin Wars
Also known as: Penguin-Kun Wars Vs. (JP), King of the Zoo (EU) Developer: ASCII Publishers: ASCII (JP), Nexoft (US), Nintendo (EU) Platform: Game Boy Released in JP: March 30, 1990 Released in US: July 1990 Released in EU: 1990 This game has a hidden sound test. This game has a hidden level select.

Level Select

At the character select, highlight the character to be chosen, hold Left + B and press A to add a number to the bottom-right corner of the screen. Press Up / Down to toggle it and press A to go to the level calculated by formula: ((number-1)*4)+1, so you actually may select every 4th level in this game (1, 5, 9,...37 max).

Sound Test

At the character select, press B + Select to cycle through the game's music.

(Source: cah4e3)