The Many-Faced Mask of Mong is a magical artifact featured in the Kung Fu Panda Vol 2 story, "Divide and Conquer."
The mask was stolen from its rightful place by Su Wu of the Wu Sisters, who used it to infiltrate the Jade Palace by impersonating members of the Furious Five. She also used this ability to sow dissent among the Five, all part of her plan to seize the Belt of Cosmic Cohesion from Shifu and use it to make herself and her sisters invincible. When this plan was thwarted by Po, Su used the mask again to take the form of Tigress, gaining her skills in the process. However, when pitted against the true Tigress, she failed to match the ferocity of the noble Kung Fu Master and was defeated; the mask was then confiscated from her.
The Many-Faced Mask of Mong has the ability to change its wearer's physical characteristics completely, allowing them to pass as another being. They can also switch from one disguise to another without reverting back to their natural form. It also grants the wearer the combat skills of the being they transform into. However, the mask does not enable perfect impersonation, as it cannot simulate or replicate the personality of the being it's user takes the form of, which is what enabled Po to see through Su Wu's deception. Su Wu was also only seen using it to take forms similar in structure to her own-such as Tigress and Monkey-and it is thus unknown whether more drastic transformation are known.