Nephilim

... Oh, boy... well, here we go.

When two enemies that hate each other to the point they would despise having sex with one another have a child, they create a futanari monster with the potential to be unmatched by any monster and that could challenge the gods themselves. When an futanari that is an angel mates with any sort of demon futanari, they create a Nephilim.

Nephilim are... outcasts, to say the least. Not just from their parents, but from all monster kind. They have the strongest emotions, the hardest will, and the unsurpassed passion. These are their greatest strengths, and greatest weakness. They can grow in strength quicker than any other monster, and gain power and magic quickly. They also can gain powers from certain monsters they defeat in combat that were significant to them in some way... including goddesses. The Nephilim are usually hunted down before they can cause much harm, and brought to prison dimension Limbo, under orders of the Goddesses.

Nephilim are unique, as they are sometimes the closest thing to being a human or the furthest from them, depending on their parent. A lesser Angel and a Succubus could make a very human looking child, while a Nuckelavee and a Valkyrie could make a weird mix of a lion, centaur, angel, and a demon. Again, all dependent on the parent.

That being said, Nephilim are a one in a million chance of being born from the highly rare case when angels and demons mate, and Nephilim are infertile.