"An oval mirror in a silver frame hung on the wall."
A magic mirror in the Masked Man's cell in Pinocchio Prison. It is a two-way communication mirror made by the witch Hagetta. Most likely, it functions by placing a hand on the glass (like its counterpart- Little Bo Peep's mirror).
The mirror is mentioned in A Grimm Warning- it is unknown what happens to it after the Masked Man escapes from prison.