The following are known Action Replay Codes for Roswell Conspiracies: Aliens, Myths & Legends on Nintendo Game Boy / Color (GB / GBC). These codes were also known as GameShark Codes and in most cases will work on both devices.

Device Compatibility: Action Replay & GameShark

Public Never Aware
9100dcc0

All Aliens Exposed
9100dac0

Infinite Health
966303d0

Have All Weapons
9140f0c0

All Explosives Found
9100dbc0

Infinite Time (In Car)
9163dec0

Infinite Ammo (All Weapons)
9163ddc0

1 Hit Boss Kills
960023d0