Instructions
Complete Level 2, the Angry Aztec level, with any character to earn the key after defeating Dogadon. This key will give you access to Frantic Factory.
Walk over to K. Rool's island and jump up onto the raised platform by pressing the "A" button. Jump up onto the walkway next to the platform.
Continue walking up the circular walkway until you reach the fourth warp pad. Jump onto the warp pad and press the "A" button. This will also save the entrance to Frantic Factory for later use in the game.
Walk up the stairs to the lobby of Frantic Factory. Make sure that you have at least 15 bananas to get past the B. Locker guard and then walk up to him. Watch the cut scene or skip it by pressing the "Start" button.
Walk forward after the cut scene and you'll see Chunky Kong hanging in a cage. Continue walking until you reach the blue lever and then press the "A" button. You will then enter the Frantic Factory level.