Question:

In Changes, just before Harry turned her into a flat tire...did Arianna throw a death curse with the mumbled word he didn't recognize? 

The headache stopped by DR in Cold Days only started in the room of "Memory... Reflection."  Kinda supports the idea that the headaches' purpose is to keep him from certain trains of thought.

The immediate thought Harry had right before the "parasite" headache in Cold Days was in recollection of how Ebenezer reacted to him laying down a Sanctum Invocation on the island.  He thought "stunned"...then "horrified."  Then *BANG*...one of the double ice pick headaches instantaneously.

Technically, I think Harry has the potential for at least four things playing with his head.

1. Mab...when she gets a whim
2. Lash, if she's still in there
3. Gained knowledge from his Mother (Blood Rites) that might or might not have activation protocols upon recognition.
4. Gained knowledge from his Mother (Changes) where he receives another gem containing knowledge of the ways.
5. Perhaps an unknown party known as the parasite (my thoughts lead to Arianna's death curse).

simple though... mavra promotes BC elders because of self gain, if the elders ever come back into power she gets credit for her work and all of the BC gain more power... pragmatism can still rely on impowering your seniors

Perhaps...but she strikes me as someone who really doesn't want to answer to a higher power.  She no one's lackey as displayed by how she seems to be meddling with the Red Court like it was a toy.

assuming she wasnt there the whole time, ready to take action as needed... (like she was in BR)

or that she didnt trap the spell somehow...

heck planting a small tac nuke under the mesuem green and blowing it at the right time owuld have done the job. but letting the white council finish would have been so much better, as its deniable.

but yes, i think Cowl is very much on Mavra's 'to do' list.

hes the one that got away .

as to evil bob, I dont think mavra knows he exists. She had a chance to examine the real bob in GP, and wasnt worried. the darkhallow was in bob's head, but whatever the black court spell is shes afriad of is probably not

First of all, Kudos and applause to Cenphx for starting all this off with such a thought provoking and encompassing thread.  And, apologies if I go off on tangents periodically (Butcher's fault entirely).

I've had some time to think about the possibility that Mavra set this all up to rid the world of the Kemmerlerites.  And, it makes quite a bit of sense.  But, first, a little side issue:

None of this works if Murphy stays in town.  Harry would spill it that blackmail is going on, or she would figure it out...or more likely, she would read the lie on Harry's face.  So she has to be out of town.

Either:
1.  Mavra hired Kincaid to get Murphy out of town.
2.  A cutout of Mavra's hired Kincaid to get Murphy out of town.
3  A cutout of Mavra's hired Kincaid to take care of a little business in Hawaii  ( Kaupe the cannibal dog man was out of control) and part of the deal was a suite at the The Ritz-Carlton in Kapalua for two.  Mavra witnessed the little attraction during Blood Rites and hoped he'd take her.  Although, that's leaving too much to chance.

Face it...Kincaid was hired by Mavra to get Murphy out of town so she could have an unobstructed gun (Harry) to point at the Kemmerlerites.  Harry should just change his name to "Tool."  First, Mavra turns him into a loaded gun.  In Changes, Odin turns him into a loaded gun.  Both point him at their respective targets.

I don't think Mavra ever had Kemmerler's Word until he handed it to her at the end of Dead Beat, however.  I think she knew it was on the market (and by whom...Bony Tony) as soon as he started taking bids.  Cowl, as a Kemmerlerite, would have told her.  Getting it wasn't important because of the nature of the Darkhallow.  Cowl knew about Bob.  He might have learned about him during Grave Peril (or from Mavra).  They both, likely, had the opportunity to evaluate what he was.  Although, I think it more likely that Cowl has a previous relationship with Justin DuMourne, and was well aware of Bob's history and knowledge of Kemmerler.  He never really needed the book...but was more interested in keeping it out of Corpsetaker and Grevane's hands.  And, even that didn't matter due to his strategy during the Darkhallow. 

The simple fact of the matter is that whomever performed the Darkhallow was at their most vulnerable.  Each Kemmerlerite tried to counter this by having a sidekick.  Corpsetaker/ The Ghoul ;  Grevane/ Liverspots (and his zombie army);  Cowl/ Kumori.  One does the Darkhallow.  One watches the primary's back.  Cowl's obvious strategy was to let the other two fight it out while he stayed out of sight.  When the "last one standing" performed the Darkhallow, he would pop out and take that one down, and the Darkhallow was all his.  The wildcard was Harry.

At the same time this was all going on, Mavra goes to the Red Court (which she has been using all along) and instructs them to attack the White Council with all they've got.  It was bloody and prolonged fighting that even proceeded to poison gas at mortal hospitals.  The Red Court even violated Faerie and probably the Unseelie Accords  (of course when you payoff Ferrovax with a princely gift to look the other way...who cares).  But, the White Council must be put on the defense so they couldn't field a full team of Wardens to stop the Darkhallow before it got started.  I disagree with Ms. Duck on this issue.  She needed the Darkhallow to go all the way forward because by that time only one would be left standing...because of the vulnerability of the party performing the ritual.  If the White Council shows up in bulk, it would probably never get started, and all the Kemmerlerites wouldn't be fighting it out amoung themselves.  They would be hightailing it out of there.  Mavra's hope was that they would not provide anyone to assist Harry, which has been the norm in the past. 

As it turns out  Corpsetaker gets taken out early.  Then Grevane, while occupied controlling the Darkhallow gets taken by Carlos.   If Mavra is under a veil watching this, she's nervous at this point because the sometimes ally she wants dead (Cowl) hasn't showed himself yet.  But, she has her loaded gun (Harry) there to draw him out.  Cowl makes his play (dropping his zombie disguise) and presumably disables Harry. 

Mavra thinks this is golden.  She waits for Cowl to turn his attention to the Darkhallow.  Kumori is focussed on Harry, and she can step in and take out the final two (or three counting Kumori) individuals with knowledge of Kemmerler's Word without breaking a sweat.  But, Harry messes up her perfect plan.  He regains control of Bob, and Bob flies a dinosaur into Cowl releasing all the built up energy and power into a tree flattening shock wave.  By the time Mavra regains her senses, Harry has acquired the book, Cowl and Kumori are gone as well.  Cowl is alive, and Kumori is questionable. 

So...yeah...I agree with you that Mavra had two goals:
1.  Get the Book of Kemmerler
2.  Take out all those with detailed knowledge of The Book of Kemmerler

I don't think she had it previously.  And, I still think her goal is to return to life (I still believe Mavra to be Morgana).  But, I think Kemmerler's Word is a severe threat to wiping out the Black Court in mass....and also a clue on how to raise the Black Court in mass (sort of a reverse Darkhallow in the middle of a cemetery )

Bonus:  Kumori annagram is Miroku, which is an anime character that performs exorcisms and demon exterminations...

i agree with grandpanjandrum. cowl is out for number one. maybe he's been infected, maybe he makes schemes with other shady characters and maybe he gets tooled out sometimes but ultimately cowl is doing what he thinks is best overall. yes that involves murdering countless innocents and taking out the WC, which btw if i interpreted his DB monologue correctly has been corrupted by other necromancers and dark magic users besides himself. at the end of the day he's a classic vader archetype. why it wouldn't surprise me at all if in the end he dies fighting a larger malignancy than himself 

No where is this more obvious than when he first meets Harry.  He states something like... "I don't want to hurt you...I have a certain amount of respect for you...but I will if I have to." 

the way I seed DB is it was a trap, set by Mavra, for the necromancers. The Word was the bait, she likely had it all along. 

Oh, man...you have to explain THAT.  Otherwise, you're cruel and inhuman. 

I think everyone is missing the connection between Storm Front and Fool Moon.  The latter is just an escalation of the former.  They both are reflective of something that took place about a decade earlier.

Approximately 10 years prior to Storm Front:
Gregor is attempting a coven.  At some point, a warden of the White Council shows up and tells him to knock it off according to Charity.  This is likely Justin DuMourne or Simon Pietrovich looking for a patsy.  They found one in spades and inform Mavra.

Mavra goes to Siriothrax and asks if he is interested in acquiring Excalibur for his horde.  He’s interested, but puzzled as to how she could offer.  Mavra states that the sword will come to him.  He only has to provide the Word of Kemmerler to her once it does, for she happens to know it is part of his horde.  She tells him to cooperate with Gregor.  The arrogance of dragons never once suggests that he would lose against the wielder of Excalibur.

Soon after, Mavra shows up and starts mentoring Gregor in Black Magic, with the ambition of gaining the attention of the White God.  Soon sacrifices are taking place to Siriothrax tempting the White God to send his Sword of the Cross (specifically Excalibur).  Yet, he doesn’t come.  However, when he threatens to sacrifice a virgin to the dragon (come on, she married Michael…and he’s a prude, plus her name is Charity), Siriothrax is about to take a bite, and Michael shows up with Excalibur.

This is a win/win for Mavra.  If Michael falls, the dragon gets Excalibur and she gets The Word of Kemmerler.  If the dragon falls, she can gain the Word of Kemmerler from the Estate sale as well as other pieces of his horde.  If they are both injured sufficiently, she may walk away with both. 

What Mavra doesn’t count on is a petty thief working for John Marcone watching the obituaries in the newspaper.  Eduardo Anthony Mendoza (aka Bony Tony)  sees a death of a single male (Siriothrax) and proceeds to secure a key of some sort to a storage locker not opened since WW2.  He probably nicked it from a safe in the house.  Obviously, that’s where Kemmerler had stored Kemmerler’s Word and Nazi loot.  At this point, it is a retirement plan as he is planning on retiring in the next 10 years.  Marcone knows nothing about this little action on the side at this point.

10 years later (Just before Storm Front)
Mavra is livid, but she methodically researches who controls crime in the area around Siriothrax’s residence and eventually learns that it is Marcone’s territory.  She confronts him directly, which is likely Marcone’s introduction into the magical scene (he’s probably been wearing a huge crucifix ever since).  When Marcone tells her that he has no idea what she’s talking about, he is being truthful.  Mavra threatens to destroy his livelihood and take away his little kingdom.  Obviously, this doesn’t sit well with Marcone.  At the same time he decides to do a little research into his employees to determine who might have nicked this odd book.  It doesn’t take long to learn that Bony Tony Mendoza is shopping around two Monets, a Van Gogh and some other stuff including a weird book on necromancy.   As a peace offering, Marcone gets all three paintings, and Bony Tony can sell the rest for favors past.

Storm Front
Mavra starts her wave of terror to intimidate Marcone still assuming he has Kemmerler's Word (which is about the worst thing she could do).  Three Eye hits the streets (which was part of the black magic she is teaching Victor Sells...the other being the blood curse, which she will present to the Red Court in good time after working out the kinks) and its basis is to cut into Marcone’s profits in the drug trade.  Bianca, who controls the prostitution in the city and wants more, provides hair/blood/focus object for Tommy Thom from his constant visits to her girls.  Also, we learn later that Mavra is tutoring Bianca in magic in Grave Peril.  It starts well before that.

Marcone decides to explore his options, and takes Harry for a ride in his limo.  He starts off by suggesting Harry take a vacation (paid) and let Marcone deal with something “on his side of the fence.”  Initially, Marcone thinks this is something he can handle, and he doesn’t want Harry airing his dirty laundry in public (by exposing Nazi loot and theft).  He, also, approaches Harry for the first time to be an employee.  It doesn't go well for Marcone.  At this point, Marcone is a piker in the magic world, and doesn’t realize just what’s out there, and what Mavra is capable of. 

Marcone, eventually, sits back and lets Harry take care of business.  End of threat?  No way.

Fool Moon
Fool Moon is about Mavra turning up the heat on Marcone (in a way, a continuation of Storm Front with different pressures).  First, she uses a talisman of the Erlking that was probably available in Siriothrax’s estate sale to create the Hexenwolf belts.  These belts are presented to an FBI team (probably under a thrall).  In the soulgaze between Harry and Denton there is quite a bit of attention paid to decay, black sludge, filth and dun-colored flies.  Harry believes this reflects a worn down cop.  He is an unreliable narrator in this case.  It is the coating provided by a Black Court vampire’s thrall.

The FBI team is another patsy, just like Gregor.  They are frustrated at being able to do nothing to get Marcone behind bars.  The Hexenwolf belts open up another option, but they lose control in the process.   Their first move is to kill Spike (a trusted Lt. of Marcone).  This is just turning up the pressure.   Marcone’s response is to try and add Harry to his staff again, even though he knows it would never happen.  He realizes that he’s in WAY over his head, and needs someone who understands the supernatural world.  One book later, Gard is at his side.

Mavra sets up an elaborate effort to scare the ever living crap out of John Marcone, and force him to turn over Kemmerler's Word (even though Bony Tony still has it).  She uses the adversarial relationship with MacFinn and the FBI (under thrall) to turn up the volume to 11.  Of course, it's also possible that Cowl got wind of Bony Tony trying to sell Kemmerler's Word by this time as have all the other Kemmerlerites.  If he passed this onto Mavra, she would not intervene with the FBI, who obviously planned on serving Marcone up to the Loup Garou.

Whatever the details at the end of Fool Moon, the pressure is off in Grave Peril (the next book) for two reasons.  One...Gard is there representing Monoc Securities.  Two...Bony Tony is likely taking bids on the black market removing Marcone from the picture, and entering Cowl into the picture as Mavra's representative.  However, the fact that Bony Tony uses a portable computer drive to hide the coordinates tells me that Marcone is advising him on the supernatural world.