The following are known Action Replay Codes for WarioWare, Inc.: Mega Microgame$! 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
00070c7c
5f2b0bea
16c7a26c
d67b2b22

Infinite Lives
0086ee41
ea927bc5

Have All Levels
ce8900e2
dcbf0e71
aab8e1f2
40ed306e

All Games in Grid
9bdf9dcf
bdd5f7aa
ee4f5c18
d5ad23aa