The following are known Action Replay Codes for The Mummy Returns 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

Infinite Health
943f2dd0

Infinite Ammo
9163dace

One Hit Enemy Kills
940063d0

First Person View: Infinite Health
943f21d0

First Person View: Stop Timer
91bfd1cf

Never Reload
910628c2