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.
While on the title screen, hold the B button and enter one of the buttons combinations below to change Quote's appearance.If entered correctly, the "Press the A Button to Begin" message will flash.The codes will work for any difficulty setting.
If the Wii's date is December 24 to 26 (set in thw Wii's settings), the appearance of the character in Cave Story would change into a Christmas/Holidays costume (regardless of character selected).The character and his/her costume will be in-game and in the menu.
(This should only work on the update or European version) From the Options menu, highlight the music option (Not the volume, the one with the New/Old option) and press 1 to go forward, 2 to go back. While the music is playing you can switch between Old and New to hear the original version or the New version.
Only applies to the updated version; they are unlocked from the start in the original release.