A thousand years ago, An Yu was trapped inside the Dragon Gong. The cause for this fate is currently unknown, nor is it known how long she was already guardian of Mystery Mountain at that point. Since she turned 2,001 years old in "An Yu's Birthday," she was already 1,000 years old around the time she got trapped.

In "The Dragon Gong," the Dragon Gong in which An Yu was trapped in was moved into the museum. At that time, Night Ninja planned to use the gong in order to prevent anyone from opposing his goal of becoming the most powerful ninja. However, this was thwarted by the PJ Masks, who eventually returned the gong to the museum. Neither Night Ninja nor the PJ Masks discovered who the dragon actually was.

Eventually, in "Meet An Yu," Night Ninja stole the gong a second time and brought it to The Pagoda on Mystery Mountain. Unbeknownst to him, this was exactly what An Yu needed to free herself. She escaped the gong, returned to her human form, and resumed her duties as guardian of Mystery Mountain. you are zar the hedgehog, and you and your brother sonic the hedgehog ended up on Mystery Mountain but she has plans for them