This is an interesting Bible Study on Noah and the Nephilim, with Scripture references. The Nephilim were giants and considered to be fallen angels at the time of Noah and the Great Flood of the Earth. Because of the evil on the earth, God had the earth flooded and all mankind killed except for Noah and his family, with the animals on the Ark. There were different historic interpretations of who the Nephilim were.
Personally, I don't believe a human being today could be a Nephilim. In Biblical O.T. times they were very tall giants, and thought to be fallen angles, or supernatural beings. Of course there are God's angels today, and fallen angels or demons.