Grand Theft Auto game cheats for Game Boy

Episode skip: 

The following trick will advance the game to the next
episode of the current level. Die or get arrested 
until you have no lives remaining. When the screen
displaying your stats appears, press A to restart 
and use the same character. The next episode in the
level will be unlocked. Repeat this procedure to 
unlock all the levels. Note: Once you start the 
next episode you must pause the game and press B 
button to quit in order for the level to be stored 
in memory.

Game Shark Codes: 

You must have a 2.1 or higher version of the 
Game Shark to use these codes in a Game
Boy Color system.

Infinite Lives              01091EDA
Infinite Machine Gun Ammo   0164A1D2

Level select: 

Rename any character to "LEVELS" to unlock all 
cities. Alternately, rename any character to
"WENDY".

Infinite ammunition: 
Rename any character to "FULL".

Hidden characters: 
Rename the character "KELLY" to "SUMNER" to 
unlock the game's developers.