Puzzle Bobble 4 – Gameboy Color

Puzzle Bobble 4 - Platform: Gameboy Color

Hidden characters
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Press Up, Down, Left(2), Right, Up, A, B(2), A at the main menu. 

Hidden levels
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Press A, Left, Right, Left, A when "Push Start" appears at the 
title screen. A game character will appear in the bottom right 
corner of the screen to confirm correct code entry.