Legend says that whoever wears the amulet becomes the Monkey King. The amulet is on display at the Forbidden City Museum in China. Monkey Fist desires the Amulet so he can become the next Monkey King in the new era. He attempts to steal the amulet from the Museum. Kim Possible is waiting for Monkey Fist at the museum when he attacks. During the scuffle, the amulet is accidentally tossed around Kim's neck and it bonds with Kim in the form of a green monkey shaped tattoo on her neck. The amulet slowly transforms Kim into a monkey. It is unknown what happens to the amulet after Kim is separated from the Monkey DNA.
According to the ancient text, there is only one way to part forcefully someone from the amulet, which is a very painful way (it's never revealed what exactly).