It's not really something he can help. Being a powerful necromancer and the son of an ancient death god is going to leave its mark on one's essence.

"He's figuring it out mostly by himself with some texts he's managed to get ... somehow... from fairie. He's an utter genius when it comes to ritual magic though," Theo said. "The fair folk are the only ones who are capable of creating portals where I'm from."

The gods possibly can, but if so they've never let humanity know and they most certainly haven't let Theo know, even if he lived with two of them.