The following are known Action Replay Codes for Teenage Mutant Ninja Turtles 2: Battle Nexus on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
8b50b158
d4332121
bbb29a89
bf720e19

Infinite Health
2b772934
aa9465b7
db342c55
c7fb7c70
5be073b9
ffcefb0f
4eccfaba
d8932a80

Invincibility
4b5b12da
a8b37600
6a94fce4
f43ddcbe