Why not Victim of Night over Devour in Shadow? Is it because of the regeneration? I think that that would be more useful if you need to kill your own Treacherous Pit-Demons.

Why is AEther vial in here?

it lets the deck play like a Control deck.

Would Phyrexian Obliterator be another good bomb? Also, I think Bitterblossom should definitely be in the deck as it will power you a win if you're getting screwed, as well as decreasing your life for Death's Shadow.

I like AEther Vial - lets you flash in Death's Shadow end of turn for surprise attacks with no blockers.

I don't like Phyrexian Totem. There is nothing to ramp into, and certainly not worth 3 life off a Dark Confidant flip. I would run Herald of Torment as a threat on its own, and one that can give your threats flying, and it loses life for you!

I like the deck but you havnt updated it in a while cause there are some better cards out now like fatal push

You don't have enough creatures for Aether Vial, it's more of a dead draw than it is a way to cheat on mana. Devour in Shadow is terrible, if you really want a removal spell that makes you lose life Dismember is much better. Vendetta is just as bad as Devour in Shadow, Fatal Push is better. You can add some fetches to make revolt work. Phyrexian Totem is nothing but a homage to an old card which wouldn't be playable now and totem itself is just a worse version of said old card with nothing to ramp into. Sangrophage will kill you before it does anything useful, I know that you want to keep the spirit of sicide black but these 'undercosted beaters' are frankly quite bad. Death's Shadow is your only payoff for losing life, and with no way to find it/get it back none of these cards that make you lose life are acctually giving you an advantage. If you want a competetive deck based around Death's Shadow there are plenty of options. Vampire's Bite dosen't do enough, pumping a creature for three isn't playable unless there is another reason for it (i.e. infect), and with the amount of life this deck is losing lifelink isn't going to save you. Treacherous Pit-Dweller is a two for one in your opponents favor, I can see many games where you play it, it gets killed, and none of your creatures are big enough to attack throgh it so you need to wait until you find a removal spell. Inquisition of Kozilek hits pretty much everything you'll need to hit early game but you don't lose two life, losing life is not an advantage. It should probably be the 4-of over inquisition.

*Thoughtseize

Youre not wrong about Fatal Push and Dismember but I would like to preserve the original list.