The following are known Action Replay Codes for Mech Platoon 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
fda38827
edafd10e
85514729
62c99e14

Debug Menu
5a2c45c5
5e4daf98
cde8ae47
e0df7372

Infinite Material Rock
a2059d32
dbabfd99
e5d64637
afee8eaa
a82c24d1
fda9c018

Infinite Energy Sand
a2059d32
dbabfd99
121c17f6
92f046f4
0289b51b
39399ebe

Infinite Laser Crystal
a2059d32
dbabfd99
66408d07
861a353e
d7cfd339
29d09ab5