The following are known Action Replay Codes for The Legend of Zelda: Oracle of Seasons 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

Have All Essences of Nature
91ffbbc6

Have All Secondary Items
91ff96c6
91ff97c6
91ff98c6
91ff99c6
91ff9ac6
91ff9bc6
91ff9cc6

Infinite Rupees
9199a5c6
9109a6c6

Max Health
9140A3C6

Infinite Ore(in Subrosia)
9199A7C6
9109A8C6

Have Rod of Seasons and all 4 powers
918FB0C6

Infinite Bombs
9110AAC6

Have Master Sword
9103ACC6

Have Mirror Shield
9103A9C6

Infinite Ember Seeds
9199B5C6

Infinite Scent Seeds
9199B6C6

Infinite Pegasus Seeds
9199B7C6

Infinite Gale Seeds
9199B8C6

Infinite Mystery Seeds
9199B9C6