Press Z+Start on the title screen, and a special "Contests" option will appear on the bottom of the main menu. Inside are the Hole-in-One Contest and Password Tournament modes.

CEUFPXJ1 - Target Bullseye Tour

BJGQBULZ - Hollywood Video Tour

GGAA241H - Super Mario Open (Mario-Golf.com tournament)

0EKW5G7U - Camp Hyrule Tournament (CampHyrule.com tournament)

2GPL67PN - Bowser Jr.'s Jumbo Tourney

9L3L9KHR - Bowser's Big Blast

ELBUT3PX - Peach's Invitational

Get a "Nice Shot" with a power shot, and the game won't subtract from your power shot total.

In the Vs. Character mode, challenge the character with a letter (envelope) by them. Beat that character one-on-one to unlock the Star version of that character. If there is no letter, you are using the character that is issuing the challenge -- go back and pick a different character. (Star characters have a longer drive, but his or her "Impact" ability decreases. The four hidden characters are Star players as soon as they are unlocked.)

Collect 50 total Best Badges in Tournament mode to unlock Boo.

In the Side Games mode, complete the Shooting, Approach, and Putting challenges under all difficulty settings to unlock Petey Piranha.

Complete all the holes in Ring Attack mode with any combination of characters.

Beat the 18 holes option in Birdie Challenge. (Also unlocks One-on, One-putt mode.)

Beat the front 9 option in Birdie Challenge.

Beat the back 9 option in Birdie Challenge.

Beat the 18 holes option in Birdie Challenge. One-on, One-putt will appear in the Side Games mode. (Also unlocks Bowser Jr.)

Beat the front 9 option in One-on, One-putt mode.

Beat the back 9 option in One-on, One-putt mode.

Beat the 18 holes option in One-on, One-putt mode. When selecting Congo Canopy, the setup screen says to press Z to turn the Tournament Greens on/off.

Finish in first place to unlock a new course.

Finish in first place in all courses in Tournament mode. "Star Tournament" appears next to the Tournament mode on the Play Mode screen.