Jareth used shape shifting to spy on Sarah throughout her life after she defeated him. His preferred alternate form was an owl, which has some connections in mythology to dreams as made evident by Jareth's powers to control illusions and fabricate dream worlds through his crystal balls which is a large part of the movie. Labyrinth Wiki
The notion that Seelie were good and Unseelie were evil is actually a christianized element that doesn't really reflect the more basic nature of the Fey. The Unseelie, and all Fey, are often seen as personifications of forces of nature it was not an uncommon belief that they could take on another form. Ravens, horses, owls, dogs and even great cats. While some were tied to more esoteric concepts like storms, trees, flowers, etc; the Unseelie were often connected with things like death, decay, winter and nightmares. This is why they were considered evil, not because they were inherently bad. All Fey like all mortals were both good and bad in varying measures and there was just as much good in the Unseelie court as there was evil in the Seelie court. This didn't really jive with christianity as it took root in England (which at one time perceived all these sort of being as angels who had chosen to remain neutral during the initial battle between Lucifer and God and remained on earth instead of going to heaven or hell.)
Furthermore shape shifters, or werewolves in particular, have a number of basic origins. One of which is tied to celtic warriors who would wear the skins of animals as armor believing it gave them power. This is both a historical explanation of the were and one of the given explanations for how many Fey were able to shape shift. For example the Roane who were able to change into seals through a second skin that they could put on (a not uncommon trait for many animal-based Fey)
Another more folklorish explanation contends that all shape shifters were the result of humans who had interbred with the Fey, the result of which could create a very human looking child who had unusual gifts or magical powers but was also more intimately tied to nature which explains the stories about werewolves being affected by the cycles of the moon.
As Unseelie Prince he would be half breed. As i said, the Unseelie were not pure blooded Fey, and in this case his bloodline would likely be tied to a werewolf mother or father. As such he would possess the same abilities as those of his lineage tho changed to reflect the more monstrous nightmares that were commonly held to be servants and assassins of the Unseelie (the Slaugh). This is why i choose a more sinister looking sabertooth tiger, implying both a connection to the werewolf race in your initial post as well as the darker notions of the Unseelie.
Anyway, i am not trying to derail your thread by any means. I was just explaining why i chose that particular background and character as it fit it not only with the original folklore that inspired the Labyrinth but also tied into the mythology surrounding both the Fey, the Unseelie and the many races you added to this concept.