The new "Noah" movie has people talking about "Nephilim" (the rock monsters in the movie), which are supposed to be fallen angels which have taken on physical form. This may seem like the most fantastic part of an extraordinarily far-fetched plot, but I have been persuaded that it is probably the correct reading of some obscure bits of the Bible. Passages in Second Peter and Jude all persuade me that some of the New Testament writers actually believed that demons had taken on physical form before the Flood.
If you don't believe in demons, that makes the New Testament that much more mythological, but if you are open to the possibility that angels (and by extension, demons) might exist, then it fits into the broader story of the Bible reasonably well. The Gospels and the Book of Acts are full of references to demons and/or "demonized" humans, who routinely confess that Jesus is Lord and then are cast out. The letters of Paul are full of references to the "powers and principalities" and "forces of darkness," which he unquestionably intended to mean hostile, non-human intelligences. If you believe the Bible, you believe in demons.
But does that mean that demons can "incarnate," i.e., take on physical forms of their own as opposed to manipulating human beings? This has been an open question for centuries, as theologians have struggled with Genesis 6:2, which says that "the sons of God" took "the daughters of men" and produced offspring called the "Nephilim." The primary competing theories about this passage are (a) the "sons of God" are the line of God-fearing descendants of Adam's son Seth or (b) the "sons of God" are angels (specifically, fallen angels; see Job 1).
While I have the greatest respect for the orthodox Evangelical theologians who believe that the "sons of God" were human, I think St. Peter and St. Jude believed they were fallen angels. Given the choice between any modern theologian and an apostle, I'm going to side with the apostle. So I read Genesis 6 to say that demons took on physical form in the days before the Flood.
If you don't believe Genesis, that makes the Old Testament that much more mythological, but... what if this is one of those cases where history became legend, and legend became myth, and things that should have been remembered were washed away in the Flood? That is the premise of Ellen Gunderson Traylor's book, "Noah," which casts Poseidon as a major character--an incarnated demon whose body is destroyed by the Flood.