When I looked through the mountain lion file at my State wildlife agency ( Fish & Game) about 30% of the reports were of black panthers. I then discovered similar percentages in Maine and Vermont.
Though it is stated as fact that melanistic cougars don't exist in North America, they apparently do exist in South America.
On utube, if you search for "black panther" you will see a video of one stalking a deer, I think the video was shot in South Carolina. As evidenced by the reaction and watchfulness of the buckinthe video, there can be no doubts the cat is a big one. Wild or escaped exotic, the video is proof that some of these sightings are the real thing.