The game you didn't know you already had.
The Cutting Room Floor, a site dedicated to documenting unused content in games, recently unearthed an entire game hidden in F-Zero GX. Players can use an Action Replay device to input either a NTSC or PAL code and unlock the arcade game F-Zero AX.
The content was a difficult find, as it was hidden for almost a decade. Recent tests have found that the American Action Replay 1.06 considers the code to be invalid and the NTSC unlocked version contains some instances of Japanese text.
F-Zero AX was released in 2003, the same year as GX, and included the option to load content from a player’s GameCube memory card. It featured the usual arcade timed races and exclusive racing tracks.
Here is the NTSC code for North America:
61TA-AXPK-UAV9E
EHJV-6U30-2DTVE
NBCW-U1NV-0JDJG
HK7K-0RFW-FNQ8Y
PF4U-P5D0-862X1
7HUZ-2PJY-J5TTU
Q7PM-1678-XE7FW
YW2J-AUVE-R79V8
T6UV-03PE-1H26C
R91R-1A6J-ZXN30
1GHM-VQ7W-7HBWW
And for our PAL readers, a somewhat longer code:
Z60V-MZG0-VRAQ2
3DFJ-55T9-J5J7P
NBCW-U1NV-0JDJG
HK7K-0RFW-FNQ8Y
PF4U-P5D0-862X1
9D4X-PVXV-R3FNV
Q7PM-1678-XE7FW
UAB4-HZ2F-AW6X5
T6UV-03PE-1H26C
BN71-WCD5-DYDNW
FHW5-F3D3-B2UZ5
NJR5-FE19-GQ851
5FRQ-P6M4-096F3
85KV-QPJD-4U999
VXM8-U9Y8-URZPR
VZFH-H43M-5N6E3
G71V-JPGY-BPDDZ
GUZD-V5KT-UBKA8