Mario Golf Cheats (GameBoy Color)

On the bookshelf in the room to the right of the Director's room. 
  On the cabinet in the Club Maker's hut. 
  To the left of the Peach Castle course entrance.

One of the kids responsible for leaving golf balls scattered around the course is hiding
in the northern area of the Tiny Tots course.

To retry a hole from the beginning, before you finish the hole, save the game and exit.
When you return to the game, you'll be back at the start of the hole.

A man is hiding on the far side of the Palm Club putting green. (Note: Find all three
hidden characters for 300 points.)

Press A + B + Select + Start. (Note: If reset occurs during game, you can continue from
the saved game file.)

Defeat Putts with a custom character.

A man who says he is on your side is hiding in the western area of the Raven Woods course.

Hold Select and press A to choose a golfer.

Defeat all four champions in a match game and finish in first place in all four courses.

Finish first in the club tournaments and defeat all of the club masters.