The Magic Mirror on the Wall is a mirror with magical properties. The mirror is loosely based on the magic mirror from Snow White, alongside Disney's interpretation.
The mirror is able to answer any sort of question imaginable. The Mirror first appears in Shrek where it helps Lord Farquaad pick a princess. It appears briefly at the end of Shrek 2, as well as in Shrek Forever After.
The Magic Mirror now appears to be claimed as a TV screen, reporting the news of Shrek, Donkey and Puss in Boots being captured by the guards of Far Far Away and is seen during the song "Livin la Vida Loca".
In the alternative universe he is again being used as a TV screen announcing that Rumpelstiltskin would have an announcement to the people of Far Far Away that if they catch the ogre Shrek they get a grand reward.
The Mirror's role is no different than the first film. It still helps Farquaad pick Fiona as his princess, and is used for his amusement.
The Magic Mirror appeared in the Shrek 2 video game as a guide in the tutorial.
The Magic Mirror appears in the Shrek Forever After video game, in which the main characters can use it to teleport between Shrek's normal world and the alternate reality.