I think IF something was genuinely witnessed, it could have been a sandhill crane or large owl as some have speculated. Although I can't think of any owls that come close to the size reported. Even considering exaggeration, the largest living owls couldn't compare to the roughly six-foot-tall Mothman. Not even if we stretched our imaginations to include a remnant specimen of the extinct Giant Cursorial Owl, which lived in Cuba 10,000 years ago and stood three and a half feet tall.
So, what did the denizens of Point Pleasant, West Virigina truly see? I don't doubt that something was witnessed but too much of the story was written after the fact when it had had time to grow more complex and fanciful. Much of the Mothman's purported psychic or paranormal abilities arose from John Keel's investigation and re-interviews by UFO investigators a decade later.
I don't believe that Mothman was, as Keel has suggested, a supranatural entity from another dimension. I think the writer's presence in the area was a good example of a bad investigation; he came in with an agenda to pursue, truth be damned. There very well could have been something very weird haunting that small town on the Ohio River but because no immediate, unbiased, scientific examination was launched, we are left with only hearsay and speculation.
I'm the first to say that I believe in a lot of weird things. I just can't swallow Mothman - not entirely, anyway.