The Not-Deer is described to look like a deer from a distance. However, as you get closer to it, more of its anatomy and behavior seem off. They tend to be sited in thre Appalachian region of North America, typically in Tennesse. Their movements are clumsy, like a newborn. It's to the point its believed to be double-jointed. Their limbs are described to be longer than a deer's, and they have a barrel chest. The most defining feature however is that Not-Deers do not have eyes on the side of their head but rather the front, like a predator. It has been recorded that some even have multiple eyes. Not-Deers are known to not be scared of humans, unlike regular deer. In fact, Not-Deer tend to approach people, which is how many are able to note the oddities. However, they only attack if they're provoked.
A possible Not Deer is featured prominently in the Adventure Time episode No One Can Hear You, serving as the main antagonist. Not Deer are classified as SCP 6448 by the SCP foundation. While the origins of the Not-Deer are unclear, it is believed that the creature has its roots in Native American mythology.