The Flatwoods Monster was part of a large UFO flap in the Eastern USA at the time. I think it was some sort of small vehicle or robotic device from a larger craft.
The witnesses described a creature operating the device from within, from what I've heard.
What's the best effort made to debunk this incident? I like to check both sides of a story before I reach a conclusion about it, but so far I've only heard the case for a real event involving a strange device that emitted some kind of unusual fog, operated by an unknown being, seen by a group of witnesses.
As for Roswell - I think it's an important case because it may involve recovered technology. And the recent statements by Dr. Eric Davis and Lue Elizondo support the view that it actually involved a recovered alien craft.
In any case I tend to assume that we've recovered exotic technology from crash retrieval operations. For one thing, it would explain the extremely intense counterintelligence efforts of the last 70 years aimed at discrediting the entire subject and humiliating credible witnesses. I suspect that we would've been subjected to the same level of PsyOps if the atomic bomb had been kept classified for the last 70 years rather than having been deployed in WWII - the online science forums would have similar rules against discussion of "kooky atomic fission theory," and the news media would still be scoffing at the "those zany conspiracy theorists who think that the atom can be split and that the military is hiding such technology right now."