Prior to Calabash
Sometime after MK defeated the Demon Bull King, Yin and Jin heard about MK and knew that he would be a perfect adversary to them. So Yin and Jin made MK deliver noodles to their hideout so they can trap him in the Calabash.
After Jin made a mistake to make Mei's Calabash counterpart tell MK that she loves him, Yin attempts to take the Calabash from him, as he thinks that Jin is just going to tell MK that everything's perfect again. But instead, Yin decided to look through their scheme book to go through the plan.
Once MK broke free from the Calabash, Yin and Jin told him about themselves and how he got trapped in the Calabash. Although, when MK attempt to fight them, Yin and Jin escaped.
After MK joined the Great Wall Race, Yin and Jin remind him that they are in the race as well. However, once the Demon Bull King and Princess Iron Fan joined, Yin and Jin quitted the race and became the announcers.
During the race, Yin and Jin commented on the racers and what they did until MK and Mei won the Great Wall Race.
Like his brother, Yin acts intimidating to other people who are unaware of him so he can make them think as a major threat, as he was scared of MK at first until the latter questioned who the Horn Demons were.
In "The Great Wall Race", it was revealed that Yin would rather make competitions difficult for people than win, as the Jin and Yin wanted to compete in the Great Wall Race but decided to become the commentators and change the course when the Demon Bull King and Princess Iron Fan joined.
Yin looks just like his brother except he has blue skin, blue horns and silver hair.
Yin wears a black armor collar, cross straps with a silver emblem, and black pants.
The Calabash was an ancient relic that allowed the user to imprison the Calabash's victims in a different universe. It was used by Jin and Yin to trap MK and imprison him there.
Via the Calabash
In Journey to the West