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Mario Golf
Password Screen:
At the main menu, highlight the option labeled "Club House" and press Z+R+A at the same time.

Extra Characters:
Beat any versus mode character to unlock them as playable.

Toad Highlands Tournament:
Put in KPXWN9N3 as a password.

Automatic Hole In One:
When you take a swing to hit the ball, press Up-C, Down-C, Left-C, Left-C. You will get a hole in with no regards to which way you hit the ball.

First Camp Hyrule Cup:
Enter oEQ561G2 as a password at the "Code Entry" screen to play a tournament on the Koopa Cup course with Donkey Kong.