The following are known Action Replay Codes for Snoopy Tennis 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

P1 Max Score
910926c3
910927c3
910928c3

P1 Score 0
910026c3
910027c3
910028c3

P2 Max Score
910929c3
91092ac3
91092bc3

P2 Score 0
910029c3
91002ac3
91002bc3

Unlock All Characters
910bcac4
910accc4

Unlock All Levels
9100b9c4
9100bac4
9100bbc4
9100bcc4