The following are known Action Replay Codes for Altered Beast: Guardian of the Realms on Nintendo Game Boy Advance (GBA).
These are Action Replay Version 3 (V3) Codes.
The codes should work with the region specified but may work for other regions as well.
Infinite Health
57e4d468...
Category
Title
Hacker
Code
Notes
Top
(M) Must Be On
Codejunkies
C964F167 53B4AC11
E0785743 EFCCB161
Top
Access All Realms
MadCatz
5ED0AFD7C0E6
Top
Have Max Score...
Control main menu
Press Start at the title screen. Hold L or R at the main menu to control the background's movement. Hold either button longer to move it faster.