I may be dumb and just not see it while it's right in front of me, but how does the deck create an infinite combo?

@clown_baby:

There are 3 components to the infinite combo:

1. The Gitrog Monster himself. His 3rd ability allows me to draw a card whenever land is put into my graveyard.
2. One of my discard outlets (ex. Wild Mongrel). I can use these to discard any card I want at instant speed.
3. Dakmore Salvage. A land with Dredge 2 that allows me to mill myself for 2 instead of drawing a card.

The Sorcery speed combo:

The loop begins with Gitrog and a discard outlet on the board, and either Dakmore Salvage in my hand, or Dakmore Salvage in the graveyard and a different land in my hand. I discard Dakmore Salvage (or the other land if Dakmore Salvage is in my graveyard) using my Wild Mongrel (or other discard outlet). Since a land has hit my graveyard, Gitrog's 3rd ability activates allowing me to draw a card. Since Dakmore Salvage is in my graveyard, I can replace that draw trigger with a Dredge 2 trigger. This mills me for 2 and returns Dakmore Salvage to my hand. Finally, Wild Mongrel gets +1/+1 (this does not actually matter since Wild Mongrel will never actually attack or do anything. However, him gaining +1/+1 is relevant as it circumvents the Four Horseman fallacy as the board-state is being changed. In other words, I cannot get a game-loss for slow-play). We have now returned to the beginning of the loop. The Gitrog Monster as well as our discard outlet are on the board, and Dakmore Salvage is in my hand. The only significant thing that has changed is that we have milled ourselves for 2. We can repeat this loop an mill ourselves infinitely. Anytime we mill a land, we can additionally draw a card. This will reduce the number of cards in our library. However, we never have to worry about accidentally killing ourselves through deckout because in the deck is Kozilek, Butcher of Truth. When he is milled his 3rd ability activates, and Kozilek as well as our entire graveyard is shuffled back into the deck. In other words, we can mill ourselves forever and always have cards in our hand. Should we draw Kozilek from one of our draw triggers it's no problem at all. We can simply discard him using our discard outlet whenever we're ready to shuffle our graveyard back into our library. By repeating this process we reduce the number of cards in our library. Eventually we will have 3 cards left in our library, and everything else in our hand. The 3 cards in our library will be Kozilek, Dark Ritual (or another ritual effect), and a land. Now, when we discard Dakmore Salvage to mill ourselves for 2, we are guaranteed to mill 1 of if not both of Kozilek and the land. Our goal is to mill BOTH Kozilek and the land. Both Kozilek and the Gitrog monster's ability will trigger at the same time so we can choose the order in which they go on the stack. We will choose to draw our card FIRST and then shuffle. Well will then draw the last card in our Library, Dark Ritual, and proceed to cast it prior to the shuffle effect resolving. We then let the shuffle resolve and are once again reset to our previous state. We have a library containing 3 cards: Kozilek, Dark Ritual, and a land. However, we now have 3 black mana floating. We can repeating this process indefinitely to create infinite black mana. If we ever fail to mill BOTH Kozilek AND the land, it's no problem. If we only mill Kozilek we imply allow the shuffle effect to resolve causing our library to be reset to the original 3. Should we only mill the land we will simply use it to draw the last card in our library (Kozilek) and then manually discard him using our discard outlet to activate the shuffle effect and reset our library to the original 3. Once we have generated infinite black mana we perform the loop a 2nd time. However, this time, instead of having Dark Ritual in our library, we will put Praetor's Grasp in our library. Remember, we can choose what's in our library by discarding the cards in our hand into the graveyard prior to Kozilek's shuffle effect. We will use the same process as we used before with our new 3 card library of Kozilek, Praetor's Grasp, and a land. However, this time, instead of using Dark Ritual to generate infinite black mana, we will use our infinite black mana to infinitely cast Praetor's Grasp to exile every card in every opponent's library. Once everyone's library is milled to 0, we pass the turn and every opponent will lose one by one as they die to their draw step's draw trigger.

There's also a 2nd kill combo that functions at instant speed. The Praetor's Grasp combo is considered the "Sorcery speed" combo (since Praetor's Grasp is a sorcery). Praetor's Grasp is the go-to win combo. However, being a sorcery we can only do it on our turn. The instant speed win combo is more complex but allows us to win during our opponents turn and, most importantly, during the clean-up step. The disadvantage of the instant-speed combo is that it requires us to have 1 Green mana and 1 Black mana available at the beginning of the combo. The sorcery speed combo does not require us to have any mana open as we can use Lotus Petal to generate the 1 black mana we need to cast the first Dark Ritual.

Instant Speed Combo:

The instant speed combo uses the same concepts and loops as the Sorcery speed combo. I trust that you've read the above combo so I will not re-explain the loops, I will only explain the over-all plan. First we will use the Dark Ritual loop to turn our 1 black mana into infinite black mana. We now have 1 Green mana and infinite black. The infinite black mana will be used to cover all of the generic mana requirements of our green instants.

The important cards are: Dark Ritual, Crop Rotation, Harrow, Edge of Autumn, and Sunscorched Desert.

The loop:

First we use our 1 green mana and infinite black to cast Harrow, sacrificing a land to get 2 forests from the deck. We tap those 2 forests to generate 2 Green mana. We now have 2 Green mana and infinite black. We use 1 of our 2 green mana to cast Crop Rotation, sacrificing one of our Forests to search for Sunscorched Desert. When Sunscorched Desert enters the battlefield, it will deal 1 damage to an opponent. We now have 1 Green Mana, Infinite Black Mana, and Sunscorched Desert. Finally, we will use Edge of Autumn's cycling ability to sacrifice Sunscorched Desert. We are now back at the beginning of the loop. We have 1 green mana and infinite black mana. The thing that has changed this time is that an opponent has taken 1 damage. We can use this loop to infinitely trigger Sunscorched Desert dealing infinite damage to all of our opponents.

I hope that helps! Please let me know if you have any other questions about the deck!