Password screen:
At the Main Menu, select 'Clubhouse' and press A+Z+R. This will enable the password screen.

First Camp Hyrule Cup:
Enter 0EQ561G2 at the Password Screen. Donkey Kong must be selected as a golfer for this code to work.

Second Camp Hyrule Cup:
Enter 5VW689O6 at the Password Screen. Plum must be selected as a golfer for this code to work.

Special Tournament:
Enter KPXWN9N3 at the Password Screen to access a secret tournament.

Enable Luigi:
Beat Luigi in 'Get Character' Mode.

Enable Yoshi:
Enable Luigi, then beat Yoshi in 'Get Character' Mode.

Enable Sonny:
Enable Yoshi, then beat Sonny in 'Get Character' Mode.

Enable Wario:
Enable Sonny, then beat Wario in 'Get Character' Mode.

Enable Harry:
Enable Wario, then beat Harry in 'Get Character' Mode.

Enable Mario:
Enable Harry, then beat Mario in 'Get Character' Mode.

Enable Bowser:
Enable Mario, then beat Bowser in 'Get Character' Mode.

Enable Donkey Kong:
Get 30 coins in Ring Mode to enable Donkey Kong.

Enable Maple:
Get 50 birdie badges in Tournament Mode.

Enable Metal Mario:
Get all 108 birdie badges to access Metal Mario.

Alternate DK Intro:
Enable Donkey Kong, then go to the 'press start' screen. Wait for it to show the introduction. Instead of Yoshi carrying Baby Mario on his back, Donkey Kong comes out holding Baby Mario with one arm.

Left-handed golfer:
Hold L when you choose your golfer.

Extra yardage:
Keep tapping Z or A when the ball lands to pick up a few more yards.

Different outfits:
Hold any of the C-Buttons while choosing a golfer to get a different costume.

Taunt:
Press C-Up, C-Left, C-Down, or C-Right to taunt your opponent during his/her turn.

Cheer:
Press any direction on the D-Pad to cheer for your opponent during his/her turn.

GameShark Codes

Warning: Version 3.0 or higher required to use these codes.

Unlimited Power Hits P1
                    801b71f80004
   
Unlimited Power Hits P2
                    801b72b00004 
 
Unlimited Power Hits P3
                    801b73680004
   
Unlimited Power Hits P4
                    801b74200004
   
Must Be On          f10b16702400

Must Be On          f10b16702400 
 
Extra Characters    810c28e80004
                    810c28ea0006
                    810c28ec0008
                    810c28ee000a
                    810c28f0000c
                    810c28f60005
                    810c28f80007
                    810c28fa0009
                    810c28fc000b
                    810c28fe000d

Thanks to Revolution readers Jack Griffin, Nick Rodekuhr, dj_chile, Chris, Bob Martin, Steve Horsemeyer, Aly Dhala, Bruce Howard, David, ChaoticInfinity, Justin Heun, JOB 3:14, Sean Causey, Aaron Illingworth, Aaron Causey, chrisD., goldpp7, and Monty Buckley!