Check it: phaedrusxy made an evil Rainbow Servant using Nagas.
That looks interesting, but I am not too sure where the domains come from. Is there more lore on the Ha-Naga in the book?
I just made it all up, based on typical tales about snakes in (mostly Western) mythology. Trickery and Charm are kind of obvious, I think. I think everyone knows of snake charmers, and my grandfather used to tell us that snakes could "Charm" birds: somehow mesmerizing them so that the bird was incapable of flying away, while the snake slithered over to devour it. I made up the other abilities based on these kinds of things and common phrases like "snake in the grass", etc.
I don't remember why I threw Travel in there. Probably because the Ha-Naga (and all nagas?) have magical flight.
The least thematic part of the whole class is actually gaining the cleric spell list at the end... although ha-nagas do cast cleric spells as arcane spells.