Anduin already told at a lie....
https://wow.gamepedia.com/Ogmot%27s_Dream_Journal
He tells himself he is bound to throne of leading the whole of the Alliance when in actuality he doesn't have to.
I think the 5 keys are 5 different relics that we have been using through out WoW's history. It's obvious the Heart of Azeroth is one of the keys, what if the Legendary Cape in pandaria is another and are artifact weapons? What if every time we used them to stop evil they were a key being turned?
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I just had an insane thought... What if Slyvannas' boss who is Death with a capital D, is actually Yogg-Saron! Yogg spoke to Arthas and made him become the Undead Lich King, and so Yogg is on the side of death. Yogg refers to himself as "The God of Death"! Maybe all of this is leading towards Yogg making Slyvannas the Lich Queen? Maybe this is all one giant Old Gold civil war we are caught up in the middle of?!
What is the most likely scenario from me realizing this, and it being true is ALL of the old gods are teaming up to take over Azeroth (the planet). They're devouring souls of the dead to be awoken and made flesh again, and the battle for azeroth met that goal. Shadowlands xpac will be us in the land of the dead fighting old gods and undead.
it's neither, that qoute refers to azeroth itself.
see since wrath we've known that the surface and only some of the crust is where we can live, because any deeper and you start waking up the endless teeming hordes of the still sleeping faceless.
this is confirmed at the dwarven digsite in the southern barrens, the cave in icecrown at the top of the mountain in the middle, and the twilight highlands.
Just to weigh in:
“Lord of Ravens” I believe to be Ravenholdt. This will tie into “her 3rd death” as he will be used to assassinate someone, thereby “turning the key” and causing her death to usher in the Old Gods. (Little more on that later)
Boy King most likely refers to Anduin. He has been called such in game, as well as someone else pointing out the Master’s table being the supreme elements of Void, Death, etc. and Anduin being a servant of the Light. The lies are more obscure as the prophecy refers to “you” and that applies to Horde and Alliance and would have to be something that he tells each faction. I don’t remember his dialogue in Pandaria, but one of the lies could have been then, with another being the peace he seeks between Horde and Alliance. The second seems likely as Saurfang mentions 1,000 years to breach the hatred while Anduin seems to push for it and speak of it almost immediately. Twisting words (prophecies do that) could mean this second part is one of the 3 lies.
Her heart I think references Alleria. During your quest to assist her in controlling the Void, she is shown visions of her loves dead in front of her. In order to control the Void, she has to push these visions aside, figuratively emptying her heart of her love for her family and making it a crater, while the Void then fills it. (Bear with this a little longer).
“Five keys” has probably already happened and refers to the Azshara fight. There are 4 Titan consoles in the room and the HoA equaling 5 keys that light the way.
“Her third death” comes back to Alleria. She has mentioned that she already feels she has died twice, as well as others stating another example is her first death was when she disappeared and was presumed dead with her second death being embracing the Void. Her 3rd death comes back to something happening causing her to lose control of the Void, Ravenholdt assassinating her, and her 3rd death being the release of the Void energies in her that allows the Old Gods to free themselves. (Another take would be Ravenholdt assassinating Arator and possibly Turalyon and that being Alleria’s figurative 3rd death).
Quick follow up, I just saw someone else’s post and think Ravenholdt could potentially be replaced with Nathanos (leader of the Forsaken Raven banners) and him killing Arator or Alleria in protecting Syl.
“It’s surface” I have no clue, but I like the theories of the Well.