Spanky's Quest (Game Boy)

Spanky's Quest
Also known as: Lucky Monkey (JP) Developer: Natsume Publishers: Natsume (US/JP) Taito (EU) Platform: Game Boy Released in JP: April 26, 1991 Released in US: July 1992 Released in EU: 1992 This game has a hidden sound test. This game has a hidden level select.

A game featuring a monkey named Spanky, seriously.

Sound Test

Enter password 0117.

(Source: GameFAQs (AlphaX))

Level Select

Enter password 0119.

(Source: GameFAQs)