The Deck:
First created in its modern form by reddit user /u/cobblepott, the Karador Boonweaver Combo deck is one of the strongest non-blue competitive combo decks. It relies on the strength of the interaction between Boonweaver Giant and Pattern of Rebirth in order to abuse Karmic Guide and Reveillark in any number of ways in order to kill your opponents. The deck is fast, deadly and very difficult to disrupt.
The General:
While we don't really rely on casting him at all in most games, Karador just oozes value. His abilities are fairly innocuous, but undeniably powerful. He costs (1) less for each creature in your graveyard (this DOES get around commander tax, by the way), and he allows you to cast one creature from your graveyard during each of your turns. This second ability is important, as it allows us to grind through control matchups by casting threat after threat every turn, regardless of if they’re countered, to make our opponents eventually run out of answers.
Combo[]
The Boonweaver Giant Combo:
Step 1: Find a way to put Boonweaver Giant into play (Entomb + Reanimate being the fastest way to do so), Boonweaver trigger grabs Pattern of Rebirth
Boonweaver Giant with Pattern of Rebirth in play
Step 2: Play a Sacrifice Outlet (Carrion Feeder, Viscera Seer, Altar of Dementia)
Sac Outlet and Boonweaver with Pattern in play
Step 3: Sacrifice Boonweaver Giant, Pattern of Rebirth trigger grabs Karmic Guide from deck, Karmic Guide reanimates Boonweaver Giant which grabs Pattern of Rebirth
Sac Outlet, Karmic Guide and Boonweaver with Pattern in play
Step 4: Sacrifice Boonweaver Giant, Pattern of Rebirth trigger grabs Fiend Hunter from deck, Fiend Hunter exiles Karmic Guide
Sac Outlet and Fiend Hunter exiling Karmic Guide in play, Boonweaver and Pattern in graveyard
Step 5: Sacrifice Fiend Hunter, Karmic Guide re-enters play and reanimates Boonweaver Giant with Pattern
Sac Outlet, Karmic Guide and Boonweaver with Pattern in play, Fiend Hunter in graveyard
Step 6: Sacrifice Boonweaver, Pattern triggers grabbing Reveillark
Sac Outlet, Karmic Guide and Reveillark in play, Boonweaver/Pattern and Fiend Hunter in graveyard
Step 7: First sacrifice Karmic Guide THEN sacrifice Reveillark to sac outlet, Reveillark triggers grabbing Karmic Guide and Fiend Hunter, Karmic Guide trigger reanimates Boonweaver Giant and Pattern, Fiend Hunter exiles Karmic Guide
Sac outlet, Fiend Hunter exiling Karmic Guide and Boonweaver with Pattern in play, Reveillark in graveyard
Step 8: Sacrifice Boonweaver, Pattern grabs a creature (usually a Kill Piece (Blood Artist/Zulaport Cutthroat, Gray Merchant of Asphodel or if all else fails, Acidic Slime to destroy all artifacts, enchantments and lands)). Sacrifice Fiend Hunter, Karmic Guide enters play and grabs Reveillark. Sacrifice Reveillark, grab Karmic Guide and Fiend Hunter, Guide grabs Boonweaver, Hunter exiles Guide.
At this point, you either net +1 creature each loop of step 8 or you can loop Karmic Guide/Reveillark/Kill Piece until each opponent is dead. This is the fastest of the combos, and can be done as early as T1 with a god hand (Entomb, Reanimate, (Carrion Feeder/Viscera Seer), Land that produces black, Lotus Petal, (Chrome Mox with black card to exile/Mox Diamond with extra land))
Plan B[]
Boonweaver Giant plus a sacrifice outlet allows us to grab every one of the combo pieces, making him the fastest way to combo, but the deck still functions fine without him.
You can still kill the table with the combination of Infinite Pair + Sacrifice Outlet + Kill Piece, and in most games this is more reasonable or more attainable than trying to combo with Boonweaver.
Infinite Pair[]
This is the term for a set of cards that, with a sac outlet, have the ability to recur each other an infinitely large amount of times.
Sets of infinite pairs:
Sun Titan + (Fiend Hunter/Saffi Eriksdotter)
Karmic Guide + (Reveillark/Saffi Eriksdotter/Fiend Hunter)
Reveillark + (Karmic Guide/Fiend Hunter/Saffi Eriksdotter)
Sacrifice Outlet[]
Self explanatory, a card that allows you to sacrifice another creature for free.
Sac outlets:
Viscera Seer, Carrion Feeder, Altar of Dementia
Kill Piece[]
A card that, with the help of an infinite pair, can end the game.
Kill Pieces, from best to worst:
Blood Artist/Zulaport Cutthroat (life loss)
Altar of Dementia (mill) (does not win if opponents are running Eldrazi or Blightsteel Colossus)
Acidic Slime (mass destruction of artifacts/enchantments/lands) (does not technically win, but controls board to an extreme extent)