1. We have been told that Nicodemus has a very specific target in mind, ostensibly kept in the Labyrinth of Daedalus. What is Nic trying to get his hands on and why?
What Nic is trying to steal is almost irrelevant, it is what he wants it for that is important. If it is the Spear of Destiny, it is for the purpose of using against an Archangel like Uriel. Also, it is not Nicodemus who really wants the "whatsit." This time Anduriel is in the driver's seat which should give Harry a chance to outsmart him (it).
However, Nicodemus does have his own goals. Hades is the Underworld of the Ancients Greeks, which is what Nic probably is. He wants to visit with someone in Hades and perhaps find a way to take them out and leave Harry in their place.
2. Nicodemus apparently called in a marker from Mab to get Harry on the team. Does he have a specific plan for using Harry or did Mab twist his request? Which of Harry's capabilities will he admit to needing, and (given that this is Nicodemus after all), which abilities is he scheming for Harry to use?
He needs Harry's Winter icing power to deal with things like rivers of fire and potetial threats like Harpies. He may also need Harry's magic ability to help Nic make potions to speak with the shades in Hades. In the original Odyssey the dead needed a libation of blood in order to speak.
As I stated in the answer to the first question Nic wants to ditch Harry in Hades and take someone else out.
3. Jim has mentioned that the book will be "Ocean's Eleven". Who else did Nicodemus recruit? How will they interact with Harry?
I think we are going to see the Redcap again. He's real good at setting up traps and is known to be very fast on his feet. Plus Nic will have discovered Red has a grudge against Harry. Shagnasty will also be part of Nic's crew. He will be along because Nic wants some serious muscle to deal with overt threats from heavyweight creatures like the Minotaur. He also has a score to settle with Dresden. I think there is a 10% chance that Mavra will also be on the team. There really isn't anything in Hades that can harm her, with the possible exception of the Gorgon turning her to stone.
4. Harry's general method of operation is to call on his friends for help. In this book, Harry is (initially) allowed one extra backup member on the crew. Who will it be? Which of Harry's other allies will "interfere" before the plot is over?
Harry will ask for Lady Molly to be part of the team and even suggest that Mab could put a geas on her to prevent Molly from removing the parasite until Harry is finished the job. Mab will refuse this request, and Harry will chose Thomas. Molly will go along anyway and remain under a veil until the vital moment when Harry needs her most. However, while Molly will remove the parasite in time, it won't be her or Thomas who ultimately saves the day.
Murphy will appear at the point where Harry and company will emerge from Hades. She won't be carrying Fidelacchius either. She will have given the swords to Michael because she no longer considers herself to be worthy of holding them. She will oppose Nicodemus as a Denarian; who has decided the only way she can stand up to Nicodemus is to take the power offered by the Fallen in her head. She will survive and disappear at the end of the story, setting up part of the plot for the next novel.
5. This is a Denarian book, so (unlike the last "end of the world" showdown), the Swords will almost certainly be present. In fact, there have been various hints... Which Sword wielders will appear in the next book and how will their interference/help affect the plot?
Sanya has to appear as he is the last wielder of a sword still on active duty. Someone we don't know will pick up a sword and do well for a while before getting killed. The sword will not have been handed out by Murphy as she will have given them to Michael for safe keeping. Michael will pick up the dropped sword and use it until the end of the book. He won't know that he can trust Harry until he sees his friend is fighting for his life against the Denarians.
It is likely Sanya and Michael will find themselves fighting Tessa and Rosanna, but more on them later.
6. Mab is apparently against Nicodemus succeeding in this heist. In the Cold Days, we found that Mab had complex reasons for wanting Harry to kill Maeve. What are Mab's reasons in this book? Is it simple thwarting or is there something deeper?
Mab still has a score to settle with someone on Tessa's crew. She expects Tessa and Rosanna to show up and try to steal the MacGuffin from Anduriel/Nic. She wants Harry and his allies in place to deal out some harsh retribution to one or both of them.
7. At the end of Cold Days, Harry needs to stay on the island to keep his growing headaches at bay. The start of Skin Games implies that those headaches will need to be resolved by the end of the book. Who or what is causing those headaches, and how will the whole thing get resolved by the end of the book?
The parasite is Nemesis. It can't take over Harry because he is a Starborn so it is doing something else. It is growing like a tumor, but one with intelligence and will of its own to destroy Harry and everything and everyone he loves.
Molly will use her neuromancy to see exactly where the parasite is and her new Winter Power to eliminate it. Failing the ability to destroy it, she will remove it (in a frozen condition so it can't do any harm until it thaws out) and then leave it stranded in Hades.
8. One of the key components of the "Ocean's Eleven" movie is that there is a final twist/reveal. Given that we've got Nicodemus, Harry, Mab, and potentially Hades (and who knows who else) all trying to get the better of each other, if there's one thing you can count on it's some sort of last minute quintuple-cross. What will be the nature of the twist and how will it all fall out?
I think I've already got a couple of last minute double crosses in action. Tessa and Rosanna show but are foiled by Sanya and Michael, while Murphy shows up and saves Harry. Here is my final twist. While Murphy saves Harry, frustrates Anduriel, and Rosanna probably bites the dust; much to Mabs satisfaction, but Murphy will steal the MacGuffin and disappear with it. However, Harry will find the magic "whatsit" on the Water Beetle with a note from Murphy explaining why she had to do what she did.
9. (Extra Credit) There are many WAG ("Wild A$$ Guess") theories on the boards, some crazier than others. Write up to three WAG theories (or make up your own) you believe are correct that will be confirmed (or at least have evidence in favor of) in Skin Games.
We know Anna Valmont will be part of the team and Harry has to look her up. My guess is that Harry will kill the thug Nic recruited because of his thieving skills; when said thug makes a move against Harry, and will be forced to find a replacement and Anna will be available. There is a WAG (not my own) that she is carrying Lasciel's coin. I like that one.
Here's one of my own WAGS; Fix will also be on hand when Harry emerges from Hades. He won't be there to help him. He will make a serious attempt to kill Harry on the general principle that he is opposing Mab's will by opposing Harry. Harry will be forced to kill him in self-defense. Mab will heartily approve of Harry's actions which will do nothing but depress Harry. However, Mab and Harry will discover it was likely that Titania deliberately sent Fix on a suicide mission when; near the end of the book, she announces a party to celebrate the choice of her new Summer Knight, Warden Carlos Ramirez, whom she recruited after he was crippled in a fight with the Fomor.
10. (Extra Credit) This is that "free form" question where you can come up with anything else you think will be in this book. Specific quotes Harry might say (will he actually quote Ocean's Eleven? The movie will have come out already in Harry's timeline)? Tidbits about the White Council? The fate of Molly? Write down anything you want. Note that whatever you write must be specifically mentioned or hinted at in Skin Games in order to be worth credit.
Harry and Molly will visit the White Council near the end of the novel. Harry will all but be accused of using necromancy to return from the dead. He will be accused of letting a Warlock run free when he was absent. Molly will then unveil, and Harry will introduce her as the new Lady Winter and ask the senior Council to pay their respects to her. Harry and Molly will feel somewhat smug about how they handled the situation until the announcement of the new Summer Knight is read before the Council.
The Carpenter's will be reluctant to let Harry see his daughter. It is also likely she will be in school at the time the initial conversation between Michael, Charity and Harry takes place so even if they did agree Harry wouldn't be able to see her until after the business with Nicodemus is finished. After Molly sees her parents, Harry will finally meet Maggie at the end of the book.