The mirror's security channel is protected with a password.
Ask around. Maybe someone present in the room has heard the password.
Robin Loot, the skull on the bookshelf, doesn't know the password. But how about that fish?
Yeah, you would need to be able to talk to animals.
How about that Robin Loot, still?
Try to get Robin's hat.
Wear it! You can talk to the fish as a raccoon. He will tell you the password to the mirror. ?
It is Wagne.
Talk to the fish again until you talk about the mirror.