"the Watchers looked down upon the daughters of Man and saw that they were fair...they made bodies and descended down upon the Earth whereupon they laid down with the daughters of Man and made children with them.."
We know that some of those children were giants. They are the ones we heard about. The bits of history we had revealed to us then abruptly denied? You recognise the pattern yet? Most of the nephilim look as human as you or I. Some die like we do and others do not. Some must do certain thinks NOT to die. Some can do things we which gave birth to our legends of monsters. The thing is that the monsters were already here and we underestimated the vast majority of them. Nobody knows how many of them are here. The native Atlans all work for Lucifer.
Some of the 'wild' nephilim - 2nd-7th generation according to current study - don't even know their heritage until something really weird happens. Some of the others get totally confused about what they actually are until someone comes along to explain things to them. Some style themselves as vampires, werewolves or some kind of demonic Satan worshippers, if only they knew! All of these later generations - nef's as they call themselves - have a whole culture built around the native Atlan nephilim (The First) and the Fallen (Riders) which has turned them into something like rock or movie stars!
The fallen say these nefs are a very watered down version but some are still quite powerful and all have some interesting powers. Most are shapeshifters of some description.