Last night, Wizards of the Coast set up the Oracle of Theros, a promotional Twitter account whose function seems to be questions-and-answers about Theros, and through which one card has been spoiled so far. Some of those answers, cryptic though they may be, hold some insights about the coming set. Let's analyze what she has to say.
I know of no god who calls himself by that name. “@angle_man: who is xenagos is he a God?”
We now know that Xenagos is a Satyr planeswalker, and not a god - this was early proof of the vagueness-yet-accuracy of the Oracle's answers.
There are many monsters on Theros, dragons are one of them. “@LautaroLobos: are the dragon still the scorch of men?”
Unsurprisingly, yes - there are Dragons on Theros. Our traditional conception of that creature type may not factor into Greek mythology all that much, but if Innistrad, the Gothic-literature block, could have Dragons, then surely a block that's, in part, about gigantic monsters could as well.
The brave leonin warriors must answer the hero's call “@mixmastermind: What role will the Leonin play on Theros?”
While it was previously unclear whether the Leonin fell under the umbrella of the "heroic" or "monstrous" races - after all, they're in a similar position to the Centaurs, having served an ancient oppressor and not too keen on the inhabitants of the great poleis after the defeat of the Archon they fought for and their being driven into the wilds - we now know that at least some of the white heroes, and perhaps some green ones as well, will be Leonin.
They have no memory of the Underworld or their former lives, but they are not thoughtless. RT @angle_man: what do you know of the Returned?
The Returned are Therosian undead - masked zombies wrenched from Erebos's grip. And guess what - they're sapient! This means they might form some of the ranks of the black heroes, since they can apparently have job types.