By the way, in the Rowling-verse, the Prime Minister is supposed to know about the Ministry of Magic; he's the one official point of contact between Muggles and wizards. I wonder if that's also true in the canonical version?

Did you just upgrade HPMoR to canon, and downgrade the Rowling-verse to non-canon? Bwa-ha-ha!

Puzzle:

Who is ultimately in control of the person who calls himself Quirrell?

• Voldemort

If Voldemort is possessing the-person-pretending-to-be-Quirrell using the path Dumbledore & co. are familiar with, or for that matter by drinking unicorn blood, then why isn't Voldy's magic noticeably weaker than before? Quirrell seems like he could at least hold his own against Dumbledore, and possibly defeat him.

If Voldemort took control of the-person-pretending-to-be-Quirrell's body outright using incredibly Dark magic, then why would Quirrell openly suggest that possibility to the DMLE Auror in Taboo Tradeoffs I?

If Voldemort returned to life via the Philosopher's Stone, then how did he get past the 'legendary' and 'fantastic' wards on the forbidden corridor without so much as triggering an alarm?

• David Monroe

If Monroe disappeared on purpose in 1975, and has been having random other international adventures since then, and has only just now decided to teach Battle Magic at Hogwarts (thereby ensuring his demise, per the Dark Lord's curse on the position) because his zombie syndrome is worsening and he is worried about living out the year, then what is his purpose in teaching Battle Magic? Is it just for the fun of it? This seems unlikely; he is very serious about his subject and rarely indulges in jokes or in irrelevant scholastic diversions.

Is it because he expects that teaching the students Battle Magic will help them learn to fight back and resist Dark wizards? Then why did he plan so poorly for his big Yuletide speech about resistance and unity as to allow Harry to seriously disrupt it? Could someone as intelligent as Monroe, whose major goal is to sway political opinion, really only give one big political speech and then, at that speech, fail to prevent one (admittedly precocious) student from giving a moderately persuasive opposing speech? Why not, e.g., cast a silent, wandless Silencio charm on Harry? Or simply inform him that he has 30 words in which to state his backup wish, or else it is forfeit? Or pretend to honor the wish that he would teach Defense against the Dark Arts next year? All of these alternatives (plus others) seem obviously better to me than tolerating such blatant interference with his primary goal.

• Lucius Malfoy

If he had those kinds of powers, he would wield them openly and just take over Britain. Also, it's hard to imagine he wouldn't have been keeping a closer watch on his son, to the point where he would know if his son was involved in a duel and/or sitting around freezing for six to eight hours.

• Slytherin's Monster

It has mysteriously powerful lore from the ancient past, and there's no firm evidence that it was killed or locked back in the Chamber of Secrets after Voldy broke in. In fact, the person who claims that Voldy's last words to the Monster would have been Avada Kedavra is...Quirrell. Not exactly a trustworthy source if Quirrell is the Monster.

OTOH, this would be ludicrously under-foreshadowed -- canon!Monster was a non-sentient beast, and the only HPMOR foreshadowing for the Monster focused on its being very long lived and able to speak Parseltongue. It's not clear how a rationalist would deduce, from available information, that the Monster was responsible -- we have very little data on what the Monster is like, so it's very hard to strongly match the actions we observe to the actions we expect from the Monster.

• Albus Dumbledore

Lots of pieces of weak evidence point here; Dumbledore and Quirrell are two of the highest-powered wizards around, and are two of the weirdest wizards around, and have roughly the same power level, so the hypothesis that says they are both caused by the same phenomenon gets a simplicity bonus. Dumbledore is frequently absent without a good explanation; Quirrell is frequently zombie-ish without a good explanation; Quirrell is zombieish more often as Dumbledore starts to get more energetic and activate the Order of the Pheonix; I cannot think of any scenes where both Dumbledore and Quirrell are being very active at exactly the same time. Sometimes Dumbledore expresses skepticism at something Quirrell says, but I cannot think of any examples of them engaging in magical cooperation or confrontation. If they are the same person, then it is convenient that Quirrell made Dumbledore promise not to investigate who Quirrell is.

We know Dumbledore snuck into Harry's room (in his own person) and left messages for Harry warning Harry not to trust Dumbledore; perhaps Dumbledore also turns into Quirrell and warns Harry in Quirrell's body not to trust Dumbledore. It is a little unclear why Dumbledore would want to limit Harry's trust in him, but it could have to do with the idea of heroic responsibility (nihil supernum) or even just standard psychology -- if Quirrell and Dumbledore agree on something, even though Quirrell says not to trust Dumbledore, then Harry is very likely to believe it.

It is hard to imagine Dumbledore murdering Hermione in cold blood, but, as Harry has been musing, you can only say "that doesn't seem like his style" so many times before the style defense becomes extremely questionable. Dumbledore prevents Hermione from receiving a Time-Turner, was suspiciously absent at the time of the troll attack (but showed up immediately after it was complete, with just enough time in between to have obliviated Fred and George, who, conveniently, handed the Marauder's map over to the Headmaster and then forgot all about it).

OTOH, having Hermione attempt to kill Draco and then having the troll kill Hermione on school grounds is terrible for Dumbledore's political agenda -- he winds up losing support from the centrists over the attack on Draco, and losing support from everyone over incompetent security. The school, where he has been Headmaster for decades and where he must keep the Philosopher's Stone, might even be closed. It's hard to understand how putting his entire power base in grave jeopardy could be a deliberate plot on his part, nor is it easily explained in terms of feeling plot-appropriate (it doesn't) or Dumbledore's insanity (a fully general explanation).

I assume that QQ knows much more than HP about all the wizarding history and trivia.

Giving up the cloak is not enough to kill you for no reason. You die after giving it up if you've used it to live beyond your span. Dumbledore is old but not out of bounds for a wizard.

As a point of interest, does the entire lineage of which Harry is the scion derive from a single Peverell brother? In which case, a less likely alternative interpretation would be

"Peverell shall have three descendants: his son, his son/descendant (who contributed to the quest in some important way), and finally Harry, who between them shall accomplish Death's defeat".

It's not enormously likely, but it would explain why "three shall be Peverell's sons" takes up a third of the prophecy when it is has zero value as a piece of information if taken at face value.

(non-native speaker here)

I was under impression that "to counterfeit" means only "to create imperfect copies in order to fraud someone", but it seems that it also means "to deceive". Thank you!

However, Harry knows that Draco's snake is specifically a Blue Krait, and has seen it before. The probability that Quirrell would end up with a Blue Krait by pure chance is low.

1) Research wandless magic

2) Become a cat Animagus

3) Cast a True Patronus Charm while in a cat form

4) Awesome, now you can impersonate Patronus of McGonnagal and no members of Order of Phoenix can trust each other anymore!

5) Ask an Auror friend to destroy your Animagus form.

6) Become a spider Animagus

7) ???

8) Terrify people!

We do know that two people can have the same Patronus, though, so it's not a matter of shape.

In canon -- but even in canon those people who ended up with the shape of someone else's Patronus didn't seem to do so deliberately, nor with intent to deceive.

A good guess, if it's someone else than Draco. But where and when did that happen? Are you referring to Harry's comment "I thought of my absolute rejection of death as the natural order." in Chapter 46? Neither of the gentlemen present thought that was sufficient information for understanding how to cast a Patronus.