Enter the following codes on the Title Screen for the desired costume. You should see a message saying "Press the A Button to Begin" after entry.
Blue Costume
Hold B and press 1, 2, 1, 2, 1, 1, 1, Up.
Christmas Costume
Hold B and press 1, 2, 1, 2, 1, 1, 1, 2, 2, Left.
Curly
Press 1, 2, 1, 2, Down.
Halloween Costume
Hold B and press 1, 2, 1, 2, 1, 1, 1, 2, 2, +, +, -, -, Right.
Red Costume
Hold B and press 1, 2, 1, 2, 2.
Yellow Costume
Hold B and press 1, 2, 1, 2, 1, Down.
Alternate Credit Portraits and Dialog
After making the rocket that leads you to the last cave, do NOT talk to Momorin to get your booster back. Instead just take the rocket and keep your Mimiga Mask. There will be some dialog change after this point and some of the portraits displayed during the credits will be altered as well.
Alternate Endings
Perform the actions below to unlock different endings.
"Normal" ending - Complete the escape sequence after the final boss without going through the Sacred Grounds.
"Bad" ending - Leave with Kazuma in the Egg Corridor.
"Good" ending - Complete the Sacred Grounds area.
Chaco's Lipstick
After you've talked with Chaco about the Jellyfish Juice, rest in her bed. You'll wake up with Chaco in it and her lipstick in your inventory.
Curly's Underwear
If you grabbed the Map item on your way through the Mimiga Village, you can use it in the back room after fighting Curly in the Sand Zone. Doing so will reveal a secret passage. If you use the map to navigate to the end and onto the ledge on the left, you can use the "Look" button to pick up Curly's Underwear. They serve no purpose.
Early Jet Pack
The Machine Gun can be used as a "jet pack" when its at Level 3. Just jump and aim it downward to float up until your ammo runs out.
Game Modes
To unlock these modes in the UPDATED VERSION you must perform the actions below. They are already unlocked in the original version.
Boss Attack - Clear the Sanctuary in Story Mode.
Curly Story - Defeat Curly in Story Mode.
Nemesis challenge stage - Have the Nemesis.
Sanctuary Time Attack - Clear the Sanctuary in Story Mode.
Hold Out for the Spur
Once you get to Curly and beat her in the Sand Zone, avoid trading your Polar Star for the Machine Gun. Later in the game, you can trade it for the Spur -- the strongest weapon in the game.
Sound Test
This may only work with the European version or the updated US Version. in the Options menu, highlight "Music." Press 1 or 2 to navigate the tunes. You can switch between Original or New versions of the tunes.
Xmas Comes to the Cave
Play the game on either Christmas Eve or Day (set the date to December 24th or 25th on your Wii), and Quote (on any difficulty) will have a black face, green ears, and don a Christmas hat.