Commander: Vito, Thorn of the Dusk Rose. Player removal mono-black deck.

This deck works with few but letal combo that makes you remove a player or win the game, the rest of the list are cards that makes the deck faster or your opponents slower. The commander's ability of dealing damage as you gain life is powerful, but not enough to conclude a match with a normal lifegain deck, so I changed the idea of the deck. There are lots of cards that make ridiculous things with the commander's ability in one turn, not throught the whole match, so I decided to fill my deck with combos with Vito, Thorn of the Dusk Rose. I think this kind of deck takes full advantage of the commander's passive ability.

Deadly Combos

• (Vito, Thorn of the Dusk Rose) + (Exquisite Blood)
  You need to deal 1 damage to a player or gain 1 life with these pieces on the battlefield to win the game.
• (Vito, Thorn of the Dusk Rose) + (Blood Tribute)
  Casting Blood Tribute with the commander in ther battlefield and tapping a vampire as Vito, Thorn of the Dusk Rose just remove a player, no matter how much life he or she has and gives you half of the target player's life which can sustain you through the match.
• (Vito, Thorn of the Dusk Rose) + (Gray Merchant of Asphodel)
  This is an easy way to gain a great amount of life, based on your devotion. A devotion of 5 and 3 opponents means that you gain 15 life and can deal 20 damage to one player.
• (Vito, Thorn of the Dusk Rose) + (Exsanguinate)
  The combo is similar to Gray Merchant of Asphodel ability, but it is more effect the more mana you spend on Exsanguinate, thus it fits with mana doublers such as Bubbling Muck
• (Vito, Thorn of the Dusk Rose) + (Sangromancer) + (Dark Deal)
  Dark Deal has all players discard their hand and will eventually trigger Sangromancer 10-15 times on average, once for each card discarded by your opponents, which results in 30-45 life gained.
• (Vito, Thorn of the Dusk Rose) + (Wall of Blood) + (Miren, the Moaning Well)
  If you sacrifice Wall of Blood you can pay any amount of life and gain that much life back, thus triggering Vito, Thorn of the Dusk Rose. Provided that you have more life than an opponent, this process results in dealing a killing blow to that player.
• (Bolas's Citadel) + (Sensei's Divining Top) + (Aetherflux Reservoir)
  The first two pieces works togheter and makes you draw a card paying 1 life as long as you have life and make you easier to find the last combo piece or other cards. With Aetherflux Reservoir you can cast Sensei's Divining Top as long as you have cards in your grimoire each time gaining more and more life until you can pay 50 life to kill players doing 50 damage each or until your opponents die for the commander triggered ability.
• (Insidious Dreams) + (Bolas's Citadel)
  By casting Insidious Dreams you can put some cards on top of your library. By choosing first Bolas's CItadel and casting it next turn you can pay life to play all the other chosen cards the same turn, giving you a great change to kill your opponents.

Damage output is greatly increased by Gollum, Obsessed Stalker as it has the ability to have players lose life equal to the amount gained during your turns.

Other synergies

There are other cards that make the deck work better and do other little combos such as:

• (K'rrik, Son of Yawgmoth) + (Crypt Ghast or Basilica Screecher)
  K'rrik, Son of Yawgmoth makes possible to use the extort ability without paying mana, but life. Against 2 opponents at least this is still convenient because you regain the life spent while other players suffer 1 damage. This way you can benefit from the extort ability for each spell you cast. This synergy become deadly if you have Bolas's Citadel and Sensei's Divining Top as you can cast and extort it repeatedly by paying 3 life instead of mana to draw a card and gain back 3 life each time.
• (Doom Whisperer) + (Bolas's Citadel)
  Doom Whisperer's activated ability can let you get more value from Bolas's Citadel by milling cards that couldn't be played in that moment with the same efficiency of Sensei's Divining Top in terms of HP cost.
• (Vito, Thorn of the Dusk Rose) + (Wall of Blood)
  With Wall of Blood provided with Lifelink you can just block any creature by paying any amount of life and gaining it back triggering Vito, Thorn of the Dusk Rose for a big amount of damage. The Lifelink ability can be granted by Vito, Thorn of the Dusk Rose's activated ability. It is deadly, but it is difficult to realize since there would be no reason for a player attacking you while this creature is on the battlefield. However this is a great way to protect you from big creatures.
• (Sangromancer) + (Rankle, Master of Pranks)
  Triggering Rankle, Master of Pranks may have each player sacrifice a creature and discard a card, thus triggering Sangromancer 6 times for a total of 18 life gained.
• (Graveborn Muse) + (Black Market Connections)
  At the beginning of each upkeep Black Market Connections can create a creature token with Changeling, so it has every creature type including Zombie and have you draw an additional card thank to Graveborn Muse.

Saw in Half provides lots of synergies with most of the creatures of the deck, also it protects from a creature removal letting you keep two copies of the target creature.
It can be a player removal if it targets Gray Merchant of Asphodel as both copies would see a minimum of 5 devotion to black, if we assume that Vito, Thorn of the Dusk Rose is on the battlefield, resulting in 5 damages to all opponents and 15 life gained with 3 opponents for each copy for a total of 10 damage to all and 30 life gained that would kill a player with the commander's ability.
It increase the additional card draw from Graveborn Muse from 1 to 4 as both copies would see two zombie creatures.
It provides good additional card draw and lifegain effect if used on Twilight Prophet.
It represent a mana ramp option if used on Solemn Simulacrum.
It can increase the mana produced by each swamp if used on Crypt Ghast.

Enhancing mana pool

The number of Swamps you control affect the power of other cards like Cabal Coffers and Cabal Stronghold, Crypt Ghast and Bubbling Muck.

Mana doublers

• Crypt Ghast.
• Bubbling Muck
• Cabal Coffers.
• Cabal Stronghold.

Mana artifacts

• Arcane Signet
• Sol Ring
• Worn Powerstone
• Jet Medallion

Phyrexian Mana

• K'rrik, Son of Yawgmoth

Other

• Solemn Simulacrum.
• Myriad Landscape.
• Heartless Summoning reduces the cost of creatures by 2.

Draw cards or similar

Draw on demand

• Erebos, God of the Dead.
• Arguel's Blood Fast // Temple of Aclazotz
• Doom Whisperer pay life to surveil

Additional draw

• Phyrexian Arena.
• Black Market Connections
• Twilight Prophet
• Graveborn Muse
• Rankle, Master of Pranks

Sorceries and lands

• Read the Bones.
• Night's Whisper.
• Sign in Blood.
• Geier Reach Sanitarium.

Other

• Sensei's Divining Top.
• Bolas's Citadel let you play the first card of your library
• Solemn Simulacrum when it dies.
• Dark Deal

Tutors

• Vampiric Tutor
• Demonic Tutor
• Grim Tutor.
• Insidious Dreams tutors more cards and put them on top of library
• Beseech the Queen has a constraint on the number of lands you control.
• Dark Petition costs 2 if the spell mastery effect is triggered.

Removals

• Feed the Swarm can destroy an enchantment.
• New Blood takes control of target creature.
• Murderous Rider // Swift End is a creature removal and a creature.
• Baleful Mastery.
• Defile
• Dismember
• Infernal Grasp.
• Force of Despair destroys all creatures entered in the battlefield in the current turn, can be cast by discarding a black card into exile rather than paying its mana cost.
• Snuff Out
• Price of Fame
• Rankle, Master of Pranks
• Go for the Throat
• Toxic Deluge sends all creatures to graveyard even if they are indestructible, provided that you pay enough life.

Playing with graveyard

• Witch's Cottage is a land that returns one creature to the top of your library.
• Command Beacon return your commander to your hand from the command zone.
• Reanimate returns a creature from a graveyard to battlefield.
• Unearth returns a creature from graveyard to battlefield, can be used on Vito, Thorn of the Dusk Rose.
• Elixir of Immortality return all cards in graveyard to your library.

Protecting commander

• Lightning Greaves provides Shroud.
• Undying Evil provides Undying.
• Malakir Rebirth is similar to Undying Evil