Updated: Aug 31, 2018
Nephilim are the offspring of humans and gods cursed to walk the seafloor and protect both Major and Minor Geysers for eternity. If a Vapor, powerwielders in my world, tries to enter a Major or Minor Geyser the Nephilim will run after them and swat them out of the sky like a fly, instantly killing them. The reason being for this is that Vapors are forbidden to enter Geysers as stated in the commandments written on the Hedrons (from my other post). The reason for this is something you'll have to find out by reading the book series. The ancient language of the Gods written on the Hedrons states what rules Gods must abide by. Anyways, these beings cannot be killed by regular means.
There will be more designs for the Nephilim in the future (hence version one).