Observations:

[Lady Minerva]

Question:
Hylden Origins: Did they originally come from the Demon Dimension or is that simply where they ended up after messing with Janos Aldron's people?

Observation #1:
What an irony it turns out to be that it's Hylden blood that will poison the Mass. There's an army of the little monsters tending the thing. If Kain had known that beforehand, he wouldn't have had to go into that awful place
(the Eternal Prison) to find the Builder.

Observation #2:
The Seer. Does anyone who has played both BO2 and SR2 notice that the images in all the murals Raziel sees seem to diplict not Hylden, but creatures closer in appearance to the Seer. Look at those strange wing-like forms on
her back and then examine the murals, especially the one Raziel finds in
the Air Forge.

Mist Bug:
Has anyone had this problem? I find some mist for a stealth attack, go to activate the Mist gift -- and I suddenly end up elsewhere in the immediate area, usually up in the air, as if just landing from a ledge. It's like, huh?
How'd I get here ... !?

[Azrael]

Answer: (maybe not a very logical one)
Well if i don't get wrong the Hylden were from Nosgoth as the Ancients, imagine like, the Ancients live in the North and the Hylden in the south, then appeared something cool in the middle and both races wanted it, since they didn't get to any agreement they fight... but nobody knows exactly who started first. Well BO Series aren't my area, so anyone please fill my holes here :p

Observation #1:
Well it wasn't any blood, but the Blood of an Hylden Elder, like the Builder said:
The Builder:
It has a simple weakness. Blood is like poison to its system. And not any blood, but pure blood from the elder races. My blood. My blood will poison and kill the creature.
Drink from me, vampire, and use my life's blood to kill that which I created out of arrogance and pride. Kill me so that the Mass will die, and the Device will be destroyed.

Well i hope you got clarified with this one ;)

Observation #2:
Well the original Hylden were like that you see in the murals, and the ones you see are a devolution of what they once were, and the Seer (i think) its a Hybrid one, half Hylden half Vamp, or just still Hylden but evolved or devolved, depends on what you think of her look (personally i think she evolved), and i can't remember the SR2 mural of the Air Forge, it's been awhile since i passed there... but i'll check that today.

Mist Bug:
I think this is a job to Blinc :p :p