Two distinct morphologies share the name. The original Puerto Rican reports describe a three- to four-foot bipedal creature with membrane-gray skin, a row of dorsal spines, and large elliptical eyes. Mainland reports from Texas and northern Mexico describe a hairless, quadrupedal canid with an exaggerated overbite.
The unifying signature is the kill pattern: livestock found fully exsanguinated through two or three small punctures, with no consumption of the carcass and no tracks in soft ground around the body. Veterinary necropsies have repeatedly confirmed blood loss inconsistent with known predators.
Mainland specimens recovered to date have proven to be coyotes with severe sarcoptic mange — the archive treats the island morphology as the open case.