Sorry, but how can you possibly hang a merman by his ankles? Even actual people with what they call "Mermaid Syndrome" do not come equipped with ankles.
Not sure how to post a link, but that video is of one specific case of just that. This little girl is incredible. May she rest in peace.
There are only 2 other people in the world reported to have the same (dis)ability. Shiloh Pepin used hers to go somewhere in life.
So yes, because of people like Shiloh (I saw this air on television two years ago and researched it a bit), I do believe mermaids are real. But as I
stated previously, the OP's video has been debunked. It is not new.