The following are known Action Replay Codes for Klonoa: Empire of Dreams 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
6a704334
efa10d19
cad0b74e
4edfad75

Infinite Hearts
9e539a64
ae1f8c9d

Infinite Lives
5d03dd89
ca5e0f87

All Gems Vis1
48b9d490
84f6a3ca
17d4d4d3
c1508b6c
a42acb94
f0d9c711
579ca83c
8fb99d1f
320134f0
244d14b1
e463c3ea
8b031e37
5caf9178
2ba26f61

Press AR Button: Slow
dbba3a89
4cb74b94