I am personally trying to avoid making this a purely combo deck, as I already run multiple combo decks which my playgroup despises. Most of the combo's that you'll see in this deck are not fully intended, or are simply too good to not play with. (EG. Persist)
1) Nether Traitor + Phyrexian Altar + Golgari Germination (UPDATE: NO LONGER RUNNING GOLGARI GERMINATION. THIS HAS BEEN REMOVED)
How does it work? When Nether Traitor and Golgari Germination in play, you can sacrifice Nether Traitor to the altar to make yourself a single black mana. When the sacrifice trigger ends, Golgari Germination triggers putting a 1/1 creature into play. You can then sacrifice this token for another mana of your choice. When the token hits the graveyard (and then leaves play permanently), you can use your floating black mana to bring back Nether Traitor, leaving you with any mana of any color in your pool.
Why does this combo matter? You can use this to give yourself infinite mana, or more importantly - use it as a infinite sacrifice engine to give your general and your creatures infinite +1 counters. Once you have infinite mana, you can use the same combo with a card such as Mind Slash to eat your opponents hand, etc.
2) Woodfall Primus + Mazirek, Kraul Death Priest + Any sacrifice Outlet
How does it work? This is a unintentional combo. I always run Woodfall in any deck that is primarily green - the fact that this is a combo is completely unintentional. When both your general and a creature with persist are in play, you can sacrifice the persist creature - when it comes back into play, a +1 counter is put on the creature which effectively removed the -1 counter that persist gave the creature.
Why does this combo matter? If you haven't already noticed, this is a infinite sacrifice engine as the creature will keep coming back indefinitely. Used with a sacrifice outlet such as Phyrexian Altar, Woodfall Primus will destroy every non-creature permanent of your choice, AND give you infinite mana and +1 counters. Brutal.
3) Puppeteer Clique + Mazirek, Kraul Death Priest
How does it work? Same as above. Only difference is you steal every creature in opponents graveyards, instead of blowing up the board.
4) Titania, Protector of Argoth + Any Land Sacrifice Effect
How does it work? Pretty straight forward. I'm running all of the fetch lands, and a TON of other sacrificial lands in order to help abuse Mazireks ability. Fortunately these land sacrifice effects also work well with Titania.
Why does it matter? If you have 8 lands out and use Scapeshift or
Reprocess
while Titania is out, you're going to be putting x8 5/3 tokens into play. Read the freaking card, man!
5) Genesis + Survival of the Fittest (or)
Evolutionary Leap
How does it work? You chuck a creature card to Survival of the Fittest, or sacrifice a creature on the board to Evolutionary Leap. On your next upkeep, you can return that card to your hand for (3) if Genesis is in your graveyard.
Why does it matter?* It's a trick to help you tutor for what you need, or filter through your deck, which is VERY important when your deck needs to have what it needs to survive the upcoming sacrificial slaughter from Pox.
6) Killing Wave for 0.
How does it work? Killing Wave can be used as removal against our opponents, or as a sacrifice engine for ourself. Let's assume we played an Avenger of Zendikar and put 8 0/1 tokens into play. We can then play Killing Wave for a single black mana (Not paying for X) and cause all players to pay 0 life for their creatures. When it comes to our priority, you can choose not to pay 0 for as many creatures as you want, allowing those to be sacrificed, buffing the rest of our creatures. I recently discovered this play, and figured it was definitely worth mentioning!
Why does it matter? It's a way to have a sacrifice engine that our opponents cannot remove, or will expect. (Unless they eat our hands away). It's a sleazy way to jump someone out of nowhere!
7) Avenger of Zendikar + Mazirek, Kraul Death Priest + Scapeshift
How does it work? This is another funny play I found by accident. If you play an Avenger of Zendikar, you will put X tokens into play. The same (or next) turn, play Mazirek, and then play Scapeshift. This will cause you to sacrifice X lands, and will put X lands in play. As long as no one removes the Avenger of Zendikar, Mazirek will put a +1/1 counter on each creature, and Avenger will also put a +1/1 on each plant creature for each land sacrificed.
Why does it matter? I was able to sacrifice 9 lands, putting +18/18 on each plant token I had. I was able to get my x9 0/1 plant tokens to become 18/18 weapons of mass destruction out of nowhere to swing for lethal at each opponent. Like mentioned previously, this deck strives on "shotgun" style plays, which no-one expects.
8) Endrek Sahr, Master Breeder + Mazirek, Kraul Death Priest
How does it work? I often tutor for Endrek as soon as I have about 5-7 mana at my disposable. The goal is to play Endrek, and then another creature until we have about 5-6 creatures. It is important to NOT go over 7. As soon as we hit 5-6 creature tokens, we cast our general which spawns us an additional 5 tokens. This causes Endrek to sacrifice himself, immediately triggering Mazirek to put a +1/1 counter on each token that is in the battlefield.
Why does it matter? Just by casting our general, we can have (up to) 11 creatures that are 2/2's. If we have a sacrifice outlet, we could sacrifice the 5 tokens with summoning sickness to do some shenanigans, AND add +5/5 to out existing 6 creatures in play, giving us 35 damage worth of attackers that can attack the same turn. This can typically one-shot a player if they are unable to block!
9)
Necrogenesis
+ Ashnod's Altar
How does it work? You pay (2) colorless mana to exile a creature from a graveyard, spawning a 1/1 token. You then sacrifice that token for 2 colorless mana.
Why does it matter? You can constantly exile tokens from opponents graveyards until there are no other creatures to exile. Works well with Mazirek, and shuts down anyone playing reanimation based decks. (LOL KARADOR)