To find him, drown yourself in the circle of stars.
The Circle of Stars is the prison of N'zoth, in the depths of the ocean.
The king of diamonds has been made a pawn.
N'zoth manipulated Magni and us to use the Hearth to release him.
The lord of ravens will turn the key.
I'm starting to think this is Medivh. In the recent events, we learn that Wrathion seeks a way to protect the Dragonflights from the corrupting voices of N'zoth, and he ends up in Karazhan, where Medivh helps him.
Maybe N'zoth is counting on Medivh doing something and end up as another pawn, like Magni?
The boy-king serves at the master's table. Three lies will he offer you.
This is still a mystery to me. It seems to refer to Anduin, and probably means that he's another pawn, but I don't recall anything in particular that could be considered a lie.
Her heart is a crater, and we have filled it. First time we heard this we though it meant Azeroth. Now I'm pretty sure it meant Sylvannas. Since her death, over the years, she sees how all she loved is lost: her homeland, Silvermoon; her sisters' love; her hope to savethe Forsaken from extintion.
Seems like she found something that led her to the Old Gods and some promises we still don't know.
Five keys to open our way. Five torches to light our path.
Xal'atath refers to us as "the Opener... the Bringer of Truths... the Torch That Lights the Way!".
Opener: as in we use the Heart of Azeroth (the key) to open N'zoth's prison.
Bringer of Truths: as in freeing N'zoth we lead to Sylvannas revealing the truth, that she plotted with Azshara to start a war and use us all to free N'zoth.
The torches are not things like we though. They are people.
At the hour of her third death, she will usher in our coming.
Helya is the only one that comes to mind that she already died twice and is still around.
[B]From the earth, he draws strength. Our earth. Our strength.
Probably Wrathion.
Its surface blazes bright, masking shadows below.
X'era, or maybe another naaru we'd meet in the future.