Select the "Enter Code" option at the "Bonus Content" menu. Then, enter one of the following codes at the "Secret Cheat" screen to activate the corresponding cheat function. After a code has been accepted, you must then turn on the unlocked cheat at the "Secrets" menu.
All combos
Enter Swampfire, Gwen, Kevin, Ben as a code.
Goop
Enter Ben, Swampfire, Kevin, Big Chill as a code.
Infinite Aliens
Enter Ben, Swampfire, Gwen, Big Chill as a code.
Invincibility
Enter Kevin, Big Chill, Swampfire, Kevin as a code.
Level Lord
Enter Gwen, Kevin, Big Chill, Gwen as a code.