The deck uses it's demons, enchantments, and spells to lockdown and take control of the board , cruely beating and taking the life from your opposition. Most demons provide you with power at a cost. Sacrifice is the name of the game and so this deck will cause you a lot of pain in exchange for power.
HIDE First off, the commander Ob Nixilis, Unshackled. His first ability, an oppressive search control, forces an opponent to lose 10 life and sacrifice a creature when they search their library, and his second, gives him a +1/+1 counter whenever another creature dies. His first ability is a threat to tutors and fetchlands and his second ability threatens and combos with creature based sac engines. His 4/4 body isn't too bad but isn't much of a threat even with trample and flying but his other abilities are what will attract table removal
Razaketh, the Foulblooded is a sac engine tutor on a huge 8/8 body and can be integrated into other sac engine combos very easily aside from his mana cost
Withengar Unbound is much more difficult to get into play but if allowed to hit the table, becomes a huge threat with intimidate, flying and trample. He paints a target on your head and and attracts removal immediately.
Ormendahl, Profane Prince is a monster that can catch your opponents off guard. While the setup can take some time, it is well worth it. Being that the transformation is sac based, there are plenty of ways to accelerate it and, it works into other combos and strategies in the deck rather nicely.
Dread Cacodemon has a CMC of 10, but with an 8/8 body and a one-sided board wipe effect that is a ETB triggered ability, he is well worth the slot.
Lord of the Void is a threat both in it's 7/7 body with flying and it's ability to exile the top seven cards of that players library while also putting a creature from among them under your control.Exiling an opponents deck can be devastating let alone taking an opponents creature.
Xathrid Demon is a nefarious beat stick. A 7/7 with flying and trample is bad news for your enemies as is but his downside is more so for your opponents when used correctly. he is an immediate threat to the table and will win you the game if left unanswered, that said, he will paint a target on your head.
Pestilence Demon is a beast with a activated ability that can wipe out smaller creatures, kamikaze brutes or go suicidal and take everyone down. Very much in accordance with his flavor text.
Sower of Discord Demon of teams, is a way of taking out two players with one demonic stone. Although i rather like forcing the biggest threat at the table to have to protect/carry the player who is behind or the least threatening, beware the team effort to overthrow you. Fun politics! Note that loss of life is not damage, so Exsanguinate and Torment of Hailfire won't double the players.
Reiver Demon is a field wipe for nonblack nonartifact creatures and is a 6/6 flier to boot.
Reaper from the Abyss, Archfiend of Depravity, Indulgent Tormentor, and Desecration Demon apply tons of pressure on your opponents and help you lockdown the board.
Overseer of the Damned's ETB spot removal is just icing on the infernal cake that is his triggered ability of giving you 2/2 zombies for every nontoken creature dies. very useful with sac outlets
Shadowborn Demon's ETB spot removal is useful for threats and awesome with any recursion spells.
Harvester of Souls, Seizan, Perverter of Truth, Indulgent Tormentor, and Bloodgift Demon are the decks main form of card advantage.
Rune-Scarred Demon being a black staple for being a tutor on a stick with a 6/6 body and flying is a diabolical addition to the deck.
Sheoldred, Whispering One has so much synergy in this deck with her abilities and helps contribute to the control game of the deck. forcing opponents to sac a creature each of their upkeeps and bringing one of your creatures back during your upkeep is powerful. She can also be ran as the commander if Ob's tutor hate is too much of a liability.
Blood Speaker is a recurrable demon tutor which is exceptionally useful in this tribal build. Hell's Caretaker is a sac outlet as well as a way to revive fallen demons. Skirsdag High Priest is for generating sac fodder/beaters.
Crypt Ghast, Magus of the Coffers, Cabal Coffers, Cabal Stronghold, Nirkana Revenant, Gauntlet of Power, and Caged Sun are for mana acceleration
Grave Pact is the main enchantment of the deck, having great interaction with a large portion of the deck. Grave Betrayal is excellent coverage in case of a field wipe and turns spot removal into a snatching of a creature. Phyrexian Arena is a black card advantage staple. Whip of Erebos is the only way the deck has of bestowing lifelink to your demons but given most loss of life/pay life effects found in black, it's a major boon for the color. Mark of the Oni and Enslave allow you to demonically posses an opponents creature for your own devious plans. Gate to Phyrexia is for artifact removal, one of blacks weak points, as to further increase the power and flexibility of the deck.
Damnation, Plague Wind, Reiver Demon, and Dread Cacodemon are the field wipes of choice. reset the board state when needed.
Praetor's Grasp, Sadistic Sacrament, and Nightmare Incursion are for ripping decks apart from the inside to prevent combo's from happening.
Liliana's Contract is for the card draw and the possible win condition if the enchantment or enough demons are not removed.
Building a fun, flavorful deck comes before building a winning deck but I try to strike a balance between the two, that being said, any suggestions and +1's are appreciated