Alright, this is purely speculation - but I have kept asking Cox time and time again, with no answer. So I am beginning to think I stumbled on to a plot device secret. If you paid attention to the old time line very carefully and understand Dracula as a character, you will see the huge twist.
Now, the whole reason why Claudia was killed was because Gabriel needed the Dark Gauntlet. How this was done was due to the Devil Mask this unholy artifact was used to manipulate Gabriel, but what is so important about it? Well, if you understand the relationship of Dracula and Death in the old time line, you will make some odd conclusions.
1. "I fought hordes of Demon's and become strong" - Zobek
1a. "I capture evil souls so that he may devour them." - Claudia.
1b. "The Gauntlet is the key, there will be a time when you will be in great need of it." - Pan
Now, these two applications, think very carefully with what you see Gabriel do with the gauntlet through out the game and especially at the end of the Resurrection DLC when the Forgotten One; and if you guessed right now that Dark Gauntlet wields the Power of Dominance; the ability to absorb and rule over ALL monsters.
Now as for the Devil Mask? Well, lets take a minute here... The whole story was about uniting the three powers, which we all assumed was the God Mask. But we find out, the true power of the Mask was to see through God's Eyes. So we need to kick that out of the equation. The actuality of the story was to unite the power of the Lords of Shadow
- The Dark Gauntlet: Death (The power of Dominance)
- The Cyclone Boots (Still trying to figure out this explanation to this.)
- The Seraph Shoulders (I assume used to make Gabriel a partial Angel during the battle with Satan)
Now as for the Devils Mask - you will need to understand these particular quotes from Zobek/Death very carefully.
"Reap the whirlwinds Scions of Death, for here comes the Prince of Darkness."
This quote was one of prophecy, Zobek knew that Gabriel was going to slaughter The Forgotten One; this inheriting the title: Prince of Darkness.
But now we have this interesting journal entry from the journal, and you will need to read this very carefully if you understand Dracula.
"Look at him, so dark, so beautiful, he has come for his revenge and he shall have it. A killing machine without remorse, without pity. What happen to you, Gabriel? Love has blinded you but you have changed, my friend. Your quest is almost over, the dream is in sight. Now you must face death and you must defeat it. The mask is a powerful device and he who wields it can do anything! Bring back the dead, rule the world, destroy the universe, challenge God himself. You are the one, Gabriel. You are the one!"
1. Bring back the Dead
2. Rule the World
3. Destroy the Universe
5. Challenge God Himself
...This doesn't sound like the God Mask, now does it?
At the beginning of the first DLC (Reverie) you see Gabriel holding the mask. At the "secret" ending prologue, you see that Gabriel/Dracula has worn the Devil Mask for so long, it has become apart of him.
But this is all pure speculation.
"