Mario Golf
Hidden Cups
Nintendo Power Cup - Enter KPXWN9N3 on the password screen to play a tournament at the Koopa Cup course.

First Camp Hyrule Cup - Enter 0EQ561G2 as a code at the password screen to play a tournament at the Koopa Cup course with Donkey Kong.

Second Camp Hyrule Cup - Enter 5VW689O6 as a code at the password screen to play a tournament at the Toad Highlands course with Plum.
Credit Goes To: N64cc

Mario Star Course
Receive 2200 course points after unlocking the other five courses in the game.
Credit Goes To: Markus Pirkly via N64cc
 Hidden Cups
 Mario Star Course
 Fast Forward
 A Little More Yardage
 Metal Mario
 Donkey Kong
 Change Your Outfits
 Left Handed Shooting
 Password Screen
 Secret Characters(2)
 Secret Characters(1)
Fast Forward
Isn't it annoying when your golf ball just keeps on rolling slowly down a hill and takes forever to stop? This trick can help. After you hit the ball and it starts rolling just hold down the Z button to speed it up.
Credit Goes To: Krik457 via N64cc

A Little More Yardage
When the ball hits the ground, if you tap Z or A a bunch of times, the ball will move a little farther, giving you better yardage on your shots.
Credit Goes To: ZshotS via N64cc

Metal Mario
To play as Metal Mario get all 108 birdie badges in Tournament mode.

Donkey Kong
To access Donkey Kong without getting 30 stars, go to the Cheat screen and enter the code DKDABOMB.

Change Your Outfits
When you're choosing your character, you can change the outfits by holding one of the C-buttons.

Left-Hand Shooting
For a left-handed golfer, press the L button while you're choosing a character.

Password Screen
To access the password screen, highlight the fourth menu option on the main menu, then press and hold Z followed by R and A. The password inserter will appear in the next menu.

Secret Characters for 1P Mode

Secret Characters for all Modes

Credit Goes To: Desmond Choy via IGN 64