Ehe.. yeah, they're not all the same at all. So congrats, you're not a nerd and you don't know. They are all different aspects of concepts as karis just said, and Hades? That's both the underworld and the god of it in Greek mythology.
As for the card, I don't want any creature to start with Momentum -and- being Immaterial, especially not one you can buff. It's a bit too insta-win button for my taste, even if it's very expensive and thus only useful very late-game. It's just not in good taste to make a card this powerful, no matter its cost.