Hello, this is my Gitrog list, a combo focused commander.
Starting with the basics, the combo, phase 1. It is a 3 piece combo, first piece you should have is your commander, the second piece is a discard source and the third is a dredge card.
With these 3 pieces you should be able to dredge your whole deck, since there are almost 50% of lands in the deck, a 3 card dredge should get you going, because whenever you dredge a land you may discard the dredge card and dredge again, until you hit the best dredge card, Dakmor Salvage. Once you have the Dakmor, you can draw all the cards from your deck. What you need to do is to discard Dakmor, instead of drawing you dredge, if a land goes to the grave with the dredge, then you draw a card.
The goal is to leave only lands on your grimoire, then you cast something, discard Ulamog or Kozilek, whenever they go to your graveyard you shufle all your graveyard back, discard dakmor, draw a land and discard it until until you draw the ulamog and the previous casted card, and do it all again. With this combo you can cast your whole deck infinite times. By casting Lotus Petal or Dark Ritual, you get all the mana you need. Easiest way to win is Dimir Machinations infinite times, that way you exile the whole opponents decks. You still have other ways to do fun stuff, like Beast Within in all their permanents then Abrupt Decay on the beasts.
The whole deck is focused on getting the combo asap, preferably on the 4th turn. You have 7 discard sources and 5 dredge sources, with at least dredge 3, besides that you have 13 tutors that can get at least one discard or dredge piece and 2 that can get only the Dakmor Salvage. That puts the deck in a 20% chance of getting each piece of the combo, which means 1/5 cards will be a combo piece or a tutor for a combo piece, since our goal is the fourth turn, this means almost certain to posses the necessary cards with the 10 cards we draw from 1st turn until the 4th.
In order to achieve that 4th turn, I used most independent ramps with CMC 1-3, I don't like to rely upon having a forest or something like that. The ideal play would be tapped land or 1 mana ramps on the first turn, a tutor on the second, case you can't do something to control your opponent or a CMC 2 ramp. On the third a discard source, case you can't do a tutor. On the fourth you should have a dredge card, on your hand or graveyard, and a discard source in play, now we are only missing Gitrog, since you should have ramped at least once, you should be able to cast it. It's most likelly that you will do all this by the 5th turn but with luck you can do it in the 3rd~4th.
I used high sinergy cards in this deck, they are not essencial, but the spine of the deck is the Ulamog and the Kozilek, the tutors, dredge and discard sources, and of course the commander, besides that is all up to you to adapt the list to your liking, hope you guys enjoy it and if possible give it a like =)
Thank you very much for reading!
PS: Sorry if I messed the text up, english is not my primary language!