The primary villain of Theros block is Xenagos, the Reveler, the charismatic and debauched planeswalker who would be a God. Based on pictures we've seen in promotional art for Born of the Gods and Journey into Nyx, the dastardly Satyr should be getting a card in each of those sets, making this the first time a single character has been represented in different cards in each set in a block.
We have every reason to believe that the Born of the Gods Xenagos will function exactly like his multicolor god cycle-mates: An indestructible global enchantment that becomes a creature when you have sufficient devotion to each of his colors. The Journey into Nyx art, however, shows Xenagos in a quite markedly different shape, with an unnatural amount of horns, eyes gone blank and filled with the image of Nyx, longer, wilder, Super Saiyan-esque hair, and additional facepaint. This is probably a new card version, and a bigger and more explosive one at that. So what might set Supreme Xenagos apart from the rest of the gods?
- Demanding a sacrifice. Xenagos already has destructive tendencies, which will no doubt be magnified to insane proportions when he takes over the pantheon. His second god card might require sacrificing enchantments to get onto the battlefield in order to satisfy his lust for the desecration of the other gods' works.
- More than two colors. Though Mark Rosewater explicitly said there will be no three-color gods in Theros block, and though a power-drunk Xenagos would fit black-red-green quite nicely, no mention has yet been made of a five-color god that's apart from the cycles entirely. After all, if Xenagos does indeed become the ruler of all of Nyx and hence Theros, he'd technically have access to white, blue, and black magic. And a five-color god that requires devotion of at least, say, three to each color would be both difficult to pull off and epic and worthy-feeling.
- Legendary Enchantment Planeswalker Creature - Xenagos God. Okay, I mostly kid about this one - but Xenagos would definitely like to keep his planeswalker spark in his doubly-ascended form, no matter how crowded his typeline would get.