According to legend, the Imbunche was a male child kidnapped by, or sold by his parents to a Brujo Chilote (a type of sorcerer or warlock of Chiloé).
The Brujo chilote transformed the child into a deformed hairy monster by breaking his legs and twisting them over his back, applying a magic cream over the boy's back to cause thick hairs and, finally splitting his tongue to produce a forked, snake-like, tongue.
Travel writer Bruce Chatwin gives an interesting account of Chilote witchcraft and the imbunche in his book "In Patagonia".
British comic book writer Alan Moore wrote a version of the Imbunche which is very similar to Chatwin's description during his run on Swamp Thing.
In DC Comics
The Invunche is a demonic entity that arrived on the Earth plane several years ago. It was created by a South American coven of male witches known as the Brujería. Taking the form of a twisted humanoid with a backwards head and disjointed limbs, it systematically hunted down and murdered select individuals who were close to John Constantine, including the erstwhile Newcastle Crew. It's first victim was an American artist named Emma. The Invunche manifested in her studio as an image on her sketch pad. It took corporeal form and terrorized Emma to the point wherein she threw herself from her studio window.  It then murdered Sister Anne-Marie after stalking her on a train platform. . The Invunche then returned to the Brujería's Council of the Cave where it attacked John Constantine. Capturing Constantine, it dragged him down into the darkest depths of the cavern where the Brujería conducted their rituals.