Bowser's Magma Mountain stage:
Successfully complete the first six stages and collect 1000 coins. You have 
to buy things in the shop, including the key to the Magma Mountain, while 
playing in those six stages. After that, the Magma Mountain can be played. 
Get 1000 coins and you can buy the key to

Eternal Star stage:
Get 100 stars in the Magma Mountain stage. A special event will appear. The 
Eternal Star stage will appear after that. 

Special shop items:
Successfully complete the Eternal Star stage. The ending sequence will 
appear. After that, special items can be bought in the shops.

Alternate title screen:
Complete the game with a character to feature that person as the main 
character on the title screen. 

Extra songs:
Purchase the record from the Mushroom shop to unlock extra songs on the 
Bowser's Magma Mountain and Eternal Star stages. 

Get coins easily:
Select three of the characters. Then, stop at the final round of game and 
turn all the CPU players into players 2P, 3P and 4P. All stars and coins 
may now be easily collected.

Give all four characters a handicap of 50 coins at the character selection 
screen at the start of a game.

Win without playing:
Start the adventure or pot of skills game as normal. Press Start as soon as 
game play begins to display the settings screen. Press A, then choose 
"Controller Settings" Change all human players into CPU players. The game 
will play automatically. If you wish to collect any coins or stars, change 
the CPU players back into human players.

Bumper Ball Mazes 1, 2, and 3:
Complete Mini-Game Island by beating Toad at the Slot Car Derby 2 to get 
the first Bumper Ball Maze. Beat all 50 mini-games at Mini-Game Island to 
get the second Bumper Ball Maze. Set new records on both of those to 
unlock the third Bumper Ball Maze.