This deck is based around using K'rrik to cheat as much mana as possible to accrue enough value to win off of creatures alone, or to assemble enough combo pieces to finish off one or more opponents. Don't be afraid to spend a lot of your life early, since K'rrik is inherently going to become a target and you need to build up enough value or combo potential to be able to endure the targeting or win before they can focus you down. You have access to many free or heavily discounted creatures allowing you to build up a board of threats much quicker than most players, on top of K'rrik growing very quickly into a threat from all the black spell you are casting. His lifelink will often keep you alive.
Defiler of Flesh can serve as a backup if you don't think it is safe to cast your commander or he's been killed too many times but be warned that it only works with Permanant spells and can only reduce the cost by 1 mana. If you don't need a backup it can buff K'rrik or one of your flying threats and give them evasion.
You want to get either Bontu's Monument, Ayara, First of Locthwain, Aetherflux Reservoir, or one of the three extort creature (Thrull Parasite, Crypt Ghast, or Pontiff of Blight) out early, since these will give you back life for each spell (Araya and Bontu's Monument only give on creatures) you cast, allowing you to remain healthy for longer and avoid dropping too low. Get multiple or Aetherflux Reservoir and you can start going positive or netting life, which usually means you are in a position to win if your opponents can't interrupt you soon. Sheoldred, the Apocalypse will also keep you healthy if you're drawing a lot of cards, and even at her worst still offsets your life payment.
The Extort creatures (Thrull Parasite, Crypt Ghast, and Pontiff of Blight) in particular are invaluable, since you can pay 2 life for the extort costs, and then gain 3 life from the effect (If you have 3 opponents), netting you 1 life while draining your opponents 1 for each spell you cast. You can also pay actual mana to gain 3 life if you need it. Pontiff of Blight in particular is a win condition in itself, since with only a couple creatures you very quickly start netting life for each spell, and it doesn't take long to burn down your opponents with the extort damage.
When Tutoring early into the game, if you don't currently have any pressing issues that need answers to, usually you want to go get either Bolas's Citadel or Vilis, Broker of Blood. These two will give you massive card advantage and allow you to either draw or cast your way into either enough value to win or a win condition in itself. Villis can draw into discount spells like Jet Medallion and Heartless Summoning to start casting spells for no mana, drawing you more cards through his effect, allowing you to cast most of your deck and probably win the game. Be warned that you should be careful not to deck out, don't be afraid to cast a removal spell on your own Vilis to avoid this. When tutoring with Demonic Counsel you'll usually want either Vilis, Broker of Blood or Valgavoth, Terror Eater to start snowballing advantage, Bloodletter of Aclazotz if you've already got the ball rolling, Varragoth, Bloodsky Sire if you really need something else to complete your combo, or Reiver Demon if you need to get rid of a troublesome boardstate.
Bloodletter of Aclazotz synergizes quite well with most other cards in the deck. It causes the Extort creatures to net you 4 life per spell rather than just 1 (assuming that you are paying the life instead of the mana), increases the damage from extort, it makes Exsanguinate and Gray Merchant of Asphodel into possible table kills, and turns Shard of the Nightbringer into an instant kill for one player while causing you to gain life equal to their life total. It is usually a good Tutor target.
Mogis's Marauder Can allow you to give all your creatures haste and intimidate, allowing you to swing through most blockers and kill one or more players. Good for long turns off of Bolas's Citadel or Vilis, Broker of Blood to give all those Summoning sick creatures haste.
Be warned: Due to explosive starts with free creatures you will usually be the #1 target at your table, meaning that players may team up against you to exploit your lower life total and knock you out before you can combo off or spiral out of control. Be prepared for this with protection and backup plans. The infinite Combo of Exquisite Blood + Sanguine Bond
or Exquisite Blood + Vito, Thorn of the Dusk Rose
attracts a lot of hate and makes people target you to avoid an out-of nowhere win. The version of the deck that I take to my LGS has an extra swamp instead of an Exquisite Blood for this Reason.
Combos:
Exquisite Blood + Sanguine Bond
or Exquisite Blood + Vito, Thorn of the Dusk Rose
is the classic infinite combo that will win the game as soon as you gain life, or an opponent loses life.
Sheoldred, the Apocalypse + Vilis, Broker of Blood
will allow you to draw through your deck while actually netting life. Very easy to find one of the following combos after this.
Aetherflux Reservoir + Sanguine Bond
or Aetherflux Reservoir + Vito, Thorn of the Dusk Rose
can deal severe damage with enough spells, which is easier due to the heavy discounts from your commander.
Aetherflux Reservoir + Exquisite Blood
with more than 50 or more life can kill all your opponents by regaining you the life that you lose activating the second ability.
Sanguine Bond + Shard of the Nightbringer
, Shard of the Nightbringer + Vito, Thorn of the Dusk Rose
, or Bloodletter of Aclazotz + Shard of the Nightbringer
can kill a single player while gaining a large amount of life (Larger when using the bloodletter).
Peer into the Abyss + Sheoldred, the Apocalypse
can kill an opponent by making them draw 40+ cards and die from Sheoldred, the Apocalypse's effect. Alternatively, you can draw half your library and gain life equal to the number of cards drawn if you want to dig for a combo piece.
Gray Merchant of Asphodel + Vito, Thorn of the Dusk Rose
or Gray Merchant of Asphodel + Sanguine Bond
, with enough devotion can knock out a single player with the large amount of lifegain from the Merchant.
Bloodletter of Aclazotz + Gray Merchant of Asphodel
with enough devotion will kill your opponents or leave them low enough to kill by combat damage and you with a massive amount of life.
Exsanguinate with a large amount of mana from Crypt Ghast, Cabal Coffers, Cabal Stronghold, or Nykthos, Shrine to Nyx, will likely bring your opponents to low health while giving you a large amount of it. Add a Vito, Thorn of the Dusk Rose or Sanguine Bond to kill a specific opponent as well, or Bloodletter of Aclazotz to double the damage dealt and make it easier to kill.
Pontiff of Blight + K'rrik, Son of Yawgmoth + Bloodletter of Aclezotz, K'rrik, Son of Yawgmoth + Pontiff of Blight + Sanguine Bond
, or K'rrik, Son of Yawgmoth + Pontiff of Blight + Vito, Thorn of the Dusk Rose
can each end the game quickly by causing severe player damage for each creature you control every time you cast a spell. Using Bloodletter will deal 2 damage per creature to each other player while netting you 4 life per creature, while Vito and Sanguine bond will deal 3 damage to player per creature.