This is my favorite Commander deck: Mono-Black Sheoldred. It specializes in 187 creatures and several sac outlets to get the most out of Sheoldred. She can hit play very quickly, and once she does she dominates most of the game. A lot of your standard control elements are present, including discard (Mournwhelk, Sadistic Hypnotist, Myojin of Night's Reach), card draw (Moriok Replica, Phyrexian Rager, Phyrexian Gargantua, Phyrexian Arena, Necropotence, etc), creature kill (Grave Pact, Shriekmaw, Fleshbag Marauder, Damnation, etc), and tutoring.
EDIT: Made a couple of changes.
OUT: Mimic Vat, Life's Finale
IN: It that Betrays, Butcher of Malakir
A small bump. Made a few small changes and got some more foil cards for the deck. Replaced Attrition with Braids, Cabal Minion to get a feel of which is better. Attrition often falls short on my side, as there is a lot of black in my LGS, and I can't use it as a sac outlet without targets. Braids helps pressure my opponents and serves as a sac outlet on my turn, allowing me to recur something like Mournwhelk or Sundering Titan with Sheoldred and sac it to her trigger. Crucible of Worlds, Bloodghast, and Reassembling Skeleton also help out mitigate her upkeep trigger.
I'm considering replacing Planar Portal for Demonic Collusion. They're both repeatable tutors, and while Portal is instant speed, Collusion can also help me fill out my graveyard.
I've also thought about finding room for Carrion Feeder as another sac outlet, and of throwing in Barter in Blood for more It That Betrays synergy, but am at a loss of what to cut.
1 Sheoldred, Whispering One
Lands
1 Cabal Coffers
1 Urborg, Tomb of Yawgmoth
1 Phyrexian Tower
1 Volrath's Stronghold
1 Vesuva
1 Deserted Temple
1 Thawing Glaciers
1 Strip Mine
1 Wasteland
1 Boseiju, Who Shelters All
1 Bojuka Bog
1 Reliquary Tower
24 Swamp
Creatures
1 Viscera Seer
1 Phyrexian Revoker
1 Bloodghast
1 Reassembling Skeleton
1 Fleshbag Marauder
1 Phyrexian Rager
1 Moriok Replica
1 Dimir House Guard
1 Solemn Simulacrum
1 Necrotic Ooze
1 Graveborn Muse
1 Skinrender
1 Phyrexian Obliterator
1 Braids, Cabal Minion
1 Sadistic Hypnotist
1 Shriekmaw
1 Phyrexian Gargantua
1 Grave Titan
1 Massacre Wurm
1 Wurmcoil Engine
1 Geth, Lord of the Vault
1 Butcher of Malakir
1 Mournwhelk
1 Sundering Titan
1 Myojin of Night's Reach
1 It that Betrays
1 Vampiric Tutor
1 Tendrils of Corruption
Sorceries
1 Demonic Tutor
1 Beseech the Queen
1 Dimir Machinations
1 Praetor's Grasp
1 Yawgmoth's Will
1 Damnation
1 Diabolic Tutor
1 Promise of Power
1 Beacon of Unrest
1 Decree of Pain
1 Black Sun's Zenith
1 Death Cloud
Artifacts
1 Mox Diamond
1 Expedition Map
1 Sol Ring
1 Mana Vault
1 Lightning Greaves
1 Mind Stone
1 Fellwar Stone
1 Jet Medallion
1 Everflowing Chalice
1 Worn Powerstone
1 Darksteel Ignot
1 Skull of Ramos
1 Phyrexian Totem
1 Crucible of Worlds
1 Oblivion Stone
1 Nevinyrral's Disk
1 Memory Jar
1 Planar Portal
1 Hearless Summoning
1 Necropotence
1 Phyrexian Arena
1 Grave Pact
1 Dawn of the Dead
EDIT: Made a couple of changes.
OUT: Mimic Vat, Life's Finale
IN: It that Betrays, Butcher of Malakir
EDIT2:
OUT: Attrition
IN: Braids, Cabal Minion
BBB Mikaeus, the Unhallowed BBB
UG Momir Vig, Simic Visionary UG
UB Grimgrin, Corpse-Born UB
I'm considering replacing Planar Portal for Demonic Collusion. They're both repeatable tutors, and while Portal is instant speed, Collusion can also help me fill out my graveyard.
I've also thought about finding room for Carrion Feeder as another sac outlet, and of throwing in Barter in Blood for more It That Betrays synergy, but am at a loss of what to cut.
BBB Mikaeus, the Unhallowed BBB
UG Momir Vig, Simic Visionary UG
UB Grimgrin, Corpse-Born UB