The following are known Action Replay Codes for Donkey Kong Country 2 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
ca7ea291
68d37710
4d750228
8c6c156e

Infinite Lives
fa735257
febdfb3d

99 Bananas
bae922d5
20314f74

All Levels Unlocked
fbd1cb40
0975174a

Diddy: Super Jump
77fad025
36d99413
cfc711b9
0585971f