At one point, Demon Bull King married Princess Iron Fan and had a child with her, whom they named Red Son. After leaving the Netherworld, the Demon Bull King attacked a village and started destroying everything. However, when the Monkey King appeared, the Demon Bull King engaged in a battle with him, only to be defeated and imprisoned in a mountain for five hundred years until his son managed to release him and the family was reunited once again.
When Red Son told his parents about the Great Wall Race, they weren't interested in it, as they would rather continue to dig up the tomb than compete in a race. In frustration, Red Son says that he'll keep the Immortal Peach to himself if he wins the race. However, when he left, the Demon Bull King and Princess Iron Fan changed their minds so they crush their son's hopes in winning the race.
However, none of them were able to win the race, as the Demon Bull King and Princess Iron Fan had to quit the race after being briefly stuck in a mountain, and MK and Mei crashing into Red Son's race car. When Red Son claimed that he should've won the race to MK and Mei, he then realized that the prize for winning the race was actually a photo of the winner projected on the Great Wall. Red Son then lied that he already knew and leaves in anger.
After the Bull Clones were able to dig up the tomb, the Demon Bull King attempts to open it but failed, as he doesn't have enough power to open it. Luckily for him, Red Son stated that only a magical key can unlock the tomb and knew where to find it.
While MK and Mei were having fun with the Skeleton Key, Red Son takes the key from them and escapes. But was stopped by them when they destroyed his Inferno Truck. However, Princess Iron Fan arrives and engages in a battle with MK and Mei until she defeats them, allowing Red Son to get the Skeleton Key again and escape with her.
Once Princess Iron Fan and Red Son were able to retrieve the Skeleton Key, the Demon Bull King uses it to unlock the tomb. However, Red Son discovered that there was nothing inside but bones until he and Princess Iron Fan watch the power source going inside the Demon Bull King's armor, taking control of the Demon Bull King and the Bull Clones.
During the Chinese New Year, DBK ended up having to run a food stand with Red Son and when the Shoe Store Assistant complained to Red Son and demanded to see the stand's manager he took off upon seeing DBK. Unlike his son, he was not excited at all with his new non evil job and was later kidnapped by the Spider Queen's minions although Red Son managed to escape with a sample of the spiders' venom and had no choice but to ask Mk's team for help since he had no one to turn to.
Princess Iron Fan reluctantly became a judge at a food compatition between Speedy Panda and Pigsy's Noodles. MK and Pigsy immediately accused her of conspiring against them but she brushed them off, claiming that she was only there due to a debt she apprarently owed to Yin and Jin before muttering that she "should've never made that blood oath". After seeing how disgusting the brothers' food seemed and Tang vomiting after eating it she refused to try it but ate a small bit of Pigsy's food and was visibly delighted by it. Nevertheless she still voted for Speedy Panda. After a fight among the restaurant employees broke out, a bored Princess Iron Fan says that she "should've never came back this season".