At the Flaming Foundry, the Bull Clones continued to dig up the energy source that the Demon Bull King discovered until one of them manages to reveal the tomb. However, once they did, the Demon Bull Family attempted to open the tomb but failed, as it acquired a magical key to unlock it.
After receiving the key, MK and Mei used it to go to several places in Megapolis and have fun until MK realizes what the key is really capable of. Unfortunately, after MK and Mei pulled a prank on Pigsy by using the key, Red Son steals the key from MK and escapes by using his Inferno Truck. Although, MK and Mei goes after Red Son and manages to get the key back until Princess Iron Fan arrives and fights off MK and Mei, allowing Red Son to get the key again and escape with her.
At the Flaming Foundry, the Demon Bull King uses the key to open the tomb and sees what's inside it. However, once he did, he, Princess Iron Fan, and Red Son realized that there was nothing inside but bones until the energy source went inside the Demon Bull King's armor, taking control of the Demon Bull King and the Bull Clones.