He snorted quietly, and then said, “Not shifting.
He knows more than any man alive about dealing
with rage over injustice and being unfairly
wronged. Don’t get me wrong. I think it’s admirable
that you have those kinds of feelings, and choose
to do something about them. But they can do
terrible things to a man, too.” His face was distant
for a moment, his eyes focused elsewhere.
“Terrible things. He’s been there. I think if you
spent some time with him, you’d benefit by
it.”

   “It’s laced with . . . some kind of contagion
focus, I think.”
   I nodded. She was talking about magical
contagion, not the medical kind. A contagion focus
was something that formed a link between a
smaller amount of its mass after it had been
separated from the main body. A practitioner
could use it to send magic into the main body, and
by extension into all the smaller foci, even if they
weren’t in the same physical place. It was sort of
like planting a transmitter on someone’s car so
that you could send a missile at it later.
...
   “The contagion looks like a simple compulsion
meant to make the victim drink more, but it’s really
a psychic conduit.”
...
   “A psychic conduit?” Murphy asked. “What’s
that?”
   “It’s like any electrical power line,” I said. “Except
it plugs into your mind—and whoever is on the
other end gets to decide what goes in.”
...
   “So do what you do. Put the whammy on them,
and let’s track them down.”
   I grimaced and shook my head. “I don’t dare,” I
told her. “All I’ve got to track with is the beer itself.
If I try to use it in a spell, it’ll open me up to the
conduit. It’ll be as if I drank the stuff.”
...
   “That’s what the psychic conduit links them to,” I
said. “To Dionysus. To the god of revels and
ecstatic violence.”

   “I am the doubt that wards away sleep. I am the
flaw that corrupts, the infected wound, the false
fork in the trail. I am the gnawer, the worm in the
book, the maggot that burrows in the mind’s eye.”
   “I am He Who Walks Beside.”

   “These mortal notions,” Maeve said. “Good, evil,
love. All those other things your kind natter on
about. Are they perhaps contagious?”
   I rose with her, politely. “Some would say so,” I
told her.
   She grimaced. “In the time since her death, I
have often thought to myself that Aurora was
stricken with some mortal madness. I believe the
Queen of Air and Darkness has been taken by a
similar contagion.”

   “Sir Knight, you must have seen it. You must
have seen the contagion spreading. It has been
before your eyes for years.”
   “I haven’t seen . . .” Then I paused. My head
started adding things together. “You . . . you aren’t
talking about a physical disease, are you?”
   “Of course not,” Lily said. “It is a kind of spiritual
malady. A mental plague. An infection slowly
spreading across the earth.”
   “And . . . this plague. What does it do?” I asked.
   “It changes that which ought not change,” she
said quietly. “It destroys a father’s love for his
family by twisting it into maniacal ambition. It
distorts and corrupts the good intentions of
agents of mortal law into violence and death. It
erodes the sensible fear that keeps a weakly
talented sorcerer from reaching out for more
power, no matter how terrible the cost.”

     “Oh, oh!” Maeve said, her body twisting into a
spontaneous little dance of pure glee. “You never
saw that coming, did you, Mother? It never even
occurred to you, did it?” Her own eyes widened in
lunatic intensity. “And how will you slay me now?
Whither would my mantle go? Where is the nearest
vessel now? Some hapless mortal, perhaps,
ignorant of its true nature? The instrument of
some foe of yours, in alliance with me, ready to
steal away the mantle and leave you vulnerable?”
Maeve giggled. “I can play chess too, Mother.
Better now than ever you could. And I am now less
a liability to you alive than dead.”

• Per Bob, tulpas might have been generated in BG through collective fear and chaotic power. Tulpas are beings created from strong emotions, feelings, and thoughts. In Supernatural, a shared belief in something created that thing in the form of a tulpa.
• Harry is suffering from conjuritis, where his thoughts are manifested using ectoplasm.
• Harry's had a ton of mental trauma, to the point that he's going to have a book dedicated to it.
• Harry's more powerful than most wizards his age, and conjuritis is rare at his age, possibly to the point to the effects might not well be known.