White Stag

The White Stag was a male deer whose origins and whereabouts were steeped in mystery. According to legend, whoever caught the beast would have three of their wishes granted. Well over a year after the Archenland Conflict, High King Peter, Queen Susan, King Edmund and Queen Lucy hunted the stag in Lantern Waste, near the Lamp-post, in order for the empire to have her three wishes granted. However, they where unable to catch it, but instead unintendedly, led to their return to Earth through Digory Kirke's Wardrobe, in which they reverted into children, thus the wishes were unfulfilled. Ultimately, this had brought an end to Narnia's Golden Age and began its Dark Age.

It's been theorized that the Stag was really Aslan in disguise guiding them back to their world as they had done all that they needed to do.