The source is always magic, but in the case of vampires and immortals I think that what gives more strength to their immortality are the deaths caused to feed, I think the gods would also be considered, in season 4 it is said that the gods punish humans with catastrophes: earthquakes and fires? they said that believing in them keeps them strong, I had a theory, fearing them can also give strength, it's a form of belief too, having fear makes people believe, but I think the death of these various people in these catastrophes also feeds Immortality ( The Hollow used it to increase their dark magic, and Silas used it to maintain their psychic powers), so in a way immortals are freaks because of that detail? are they surrounded by death whether it's feeding: vampires, immortals and sirens? or causing catastrophes: the gods? I think Landon might be a different case too, I think his own death fuels immortality, (in the sense of dark energy/magic caused by death as it was for the Hollow? only in his case it's death itself that gives him energy to return from the spirit world).

I see yeah perhaps

Malivore one I want people forget me

Huh?

Malivorie place people forget you

Yeah that has nothing to do with my post though

You put malvoire on your post

The Necromancer immortality I believe comes from the magic transforming him into a being who has his foot on both planes. Similar to what Bonnie was when she was made the anchor.

Malivore immortality should have come from the fact he was a being made of mud. Basically he was born as a being without a real life-span to begin with. Plus, the beings he absorbed probably helped prolong the magic that helped kept him animated.

Phoenix may have been similar to Malivore. In the sense that it may have never original been a living being to begin with.

As for the Gods, Jen already told us their immortality comes from those that believe in them. 😎