The following are known Action Replay Codes for Gumby vs. the Astrobots 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
5ab41938
11a05979
38efc539
b172c152

Infinite Lives
1556c883
25eb3535

Invincibility
1dad321d
ed986751
ddf655e3
9bdee49c
Note: Once you get hit once this will activate.