Instructions
Go to the main menu of "Creature from the Krusty Krab."
Scroll down with the D-pad or use the Wii remote to point at the "Extras" menu. Select the "Enter Codes" sub-menu. An onscreen keyboard will appear.
Type in the cheat codes you want the costumes for. For example, the skeleton Patrick code is "BONES," the exposed brain SpongeBob costume code is "Brain" and the code for a Plankton scientist costume is "INVENT." A noise will confirm each correct cheat code entry.
Go back into the "Extras" menu. Use the Wii remote to select "Active Bonus Items" menu.
Scroll down to the bottom to find the list of costumes you unlocked. Press "A" on a costume to use it with the character. You can use only one costume at a time, so if you turn a costume "ON," the previously used costume will automatically turn to "OFF."