I believe Marcone is purely vanilla mortal. To say otherwise detracts from both his accomplishments and the thematic role he plays in the series. And I've done the whole "X-character is related to Y-character!!!" theorycrafting rigmarole in past fandoms, and I've quite learned my lesson. I'm well over it.
That said.
I do still enjoy the pet theory that Mab and Odin had a fling some centuries ago and Marcone is a resulting descendant (though still a complete vanilla mortal). This is very much a
pet theory. I don't think it's
true. I can't imagine such a revelation affecting much about the plot or the characters. And if it doesn't add to the story, I can't see it being included.
Vadderung (through Gard) pays closer attention to Marcone than I believe their business relationship necessarily calls for. In "Even Hand" Gard appeared to be on the lookout for moments when Marcone made decisions based on moral reasons over pure logic or business, and Marcone indicates this scrutiny is a very regular habit of hers ("As ever, Gard watched me.") I'd also like to bring up Vadderung's words to Harry in
Changes:
He smiled, and laughter lurked beneath his next words, never quite surfacing. "You defy beings that should cow you into silence. You resist forces that are inevitable for no more reason than that you believe they should be resisted. You bow your head to neither demons nor angels, and you put yourself in harm’s way to defend those who cannot defend themselves." He nodded slowly. "I think I like you."
One could imagine Vadderung saying the same of Marcone. At least on Marcone's better days. Let's not forget Vadderung helped sign him onto the Accords. Harry (reluctantly) needed to give Marcone better authority to help defend Chicago, and Lara most likely wanted to repay a debt for the Raith Deeps and establish a business partnership (with the possibility of business takeover via White Court vampire feeding). But we don't really know why Vadderung signed, or why he did not do so earlier. One wonders if Marcone's actions in the Raith Deeps had any impact on Vadderung's decision.
"I am... not what I was. My children are scattered around the world. Most of them have forgotten our purpose. Once the Jotuns retreated..." (
Changes, chapter 21). If we're ever going to find out Vadderung's specific interest in Marcone, it may be as soon as
Peace Talks, where Jotuns will be making their appearance.
As for Mab, we have the obvious base parallels with the cat comparisons (although Marcone has also been referred to as "reptilian") and green-colored eyes that sometimes change color (although for Marcone the change was more figurative than literal). Mab has also established a working relationship with Marcone, one which started before
Skin Game and is implied by Harry in "Jury Duty" to possibly be an ongoing affair ("He and Mab had been in cahoots lately. Maybe he’d asked her to arrange it. This had her fingerprints all over it."). Despite Harry being careful during
Small Favor to avoid stating his motivations for saving Marcone around both Gard and Demeter, Marcone by
Skin Game knows Harry did so at the behest of Mab. There are a number of ways Marcone could have learned this, but Mab may have even told him herself.
The question is
why. Mab (or Winter) has, multiple times, in
Small Favor, in "Bombshells", and in
Skin Game, executed plans which primarily benefited her goals, but also just so happened to benefit Marcone. In
Skin Game, Mab and Marcone's scheme is implied to be at least a team effort, if not mostly Mab's idea. But strangely, the first chapter of
Peace Talks seems to paint a different picture of events as far as the supernatural community is concerned, if Ramirez is to be believed. ("Marcone maneuvered Nicodemus Archleone into a corner and took everything he had, without breaking a single one of the bylaws of the Accords. Say what you will about the man, but he’s competent. It impressed a lot of people.") Why does it sound as if Marcone is getting most, if not all, the credit? Why would Mab allow this, when the events of
Skin Game would have served as a magnificent warning to all against crossing the Queen of Air and Darkness? Is it possible that Mab is personally looking into the success of one of her descendants, one who finally accomplished enough on his own power to warrant notice? Is Odin doing the same?
Eh. Who knows. That's about all I got. This post is sort of a jumbled mess, I apologize. I just wanted to get this paranoid "theory" out for the sake of discussion (and I do enjoy adding fuel to other people's flaming theories). Like I said, I don't actually believe Marcone is actually a descendant of Mab or Odin. I mean honestly, outside of Vadderung mentioning he has children, nothing I wrote above actually has anything to do with foreshadowing
familial relationships in particular. I do think there's more at work than we currently know, but I would more readily claim that it has to do with building parallels between Harry and Marcone as rivals and foils to each other.
To be honest, I think I just want it to be true for the sake of the moment when Harry gets to crack jokes about the Mafia don not being purely of Italian decent.
It also helps justify my other pet theory that Marcone wields a Sword in the Mirror Mirror 'verse. And also my other other pet theory that Hendricks's proximity to Marcone is no coincidence, as Hendricks is the latest reincarnation of the Norse hero Helgi, a silent warrior who fell in love with the valkyrie Sváfa, and the two would go on to reincarnate over and over, always reuniting as lovers (Sváfa being an earlier incarnation of the valkyrie Sigrún).