The Enchanted Mirror is a magical object that made its first appearance in the 1991 Disney animated film, Beauty and the Beast and a combo in its midquel Beauty and the Beast: The Enchanted Christmas . The mirror possesses magical abilities, allowing its user to see anything he or she wishes to see.
In The Films
It was persumably given to the Beast by the Enchantress as his only window to the outside world. When Beast lets Belle use the magic mirror, she sees her father dying in the woods, and with only hours left before the rose wilts, the Beast allows her to leave. He gives her the mirror so she can still see him, and to remember him by.
Shortly after, Belle uses the mirror to reveal the existance of the Beast to an angry mob of villagers. Gaston takes the mirror from her and uses the image of Beast to stir up the crowd. He takes the mirror all the way to Beast's castle. From there the mirror dissappears. It could have been recovered by Mrs. Potts or one of the other castle staff while they attacked Gaston and the angry mob and it may still be in Prince Adam's possession.