A boar, pretty much like any other boar in almost every way. What's unusual about it is that a briar plant has taken to it, wrapping it's root system around the boar, but also giving he boar a defensive thorn armor. The older the boar, the stronger it's thorn defense. Young piglets will actually seek out their own briar seeds as soon as they are able.
The sketch to the side is a really quick and dirty version. Based off this sketch I've managed to finish the base sprite that all it's animations will be made from, which is shown below. The briars are separate from the boar sprite.