THIS IS NOT MY DECK, I CLAIM NO RESPONSIBILITY TO THIS DECK AT ALL, THIS WAS NOT MY IDEA. I JUST REALLY LIKE THIS IDEA AND COULDN'T FIND IT ON THIS SITE, SO I FIGURED I WOULD ADD IT.
Let me give you a summary of how the deck works.
Opening Hand
There is a LOT of cheap search so an opening hand of only one land is probably acceptible as long as you have two search spells also. Pretty much any two, three, or four land hand will be ok. But every hand is improved by some search cards in it. Five lands is ok if one of the other cards is Brainstorm.
In Search Of
Your goal here is to have Basalt Monolith and Mesmeric Orb on the battlefield. The deck has plenty of search to get you there and a bit of defense along the way. You should be able to assemble the pieces by turn 3 on rare occasion, but often by turn 4 or 5. If the opponent has proper defenses, you will probably be delayed a bit while you deal with that. So it is not an especially fast combo by Legacy measurements. However unlike faster combo you have a decent amount of protection to see it through.
You also need Emrakul, Sharuum, Blasting Station, Dread Return, and three Narcomoebas anywhere in the library or graveyard. If some of these are in your hand (up to the number of Cabal Therapy in you library and grave yard) you will be able to discard them after you start going off. You do not need mana or any cards in hand. The combo takes several minutes to actually play out.
The Infinity Mill
Once you have the set up complete you can tap Basalt Monolith to untap itself as often as you like. Each time you do, Mesmeric Orb will put a single card from your library into your grave yard. Whenever you get to Emrakul its reshuffle trigger goes on the stack. In most cases, you should just let it resolve immediately. Other than that, you are looking to reveal a Narcomoeba and a Cabal Thetapy. If you reveal Cabal Therapy first, keep going. If a Narcomoeba comes first, its ability goes on the stack. Do not let it resolve yet. Keep activating the Monolith with the Narcomoeba on the stack until you see a Cabal Therapy. When that happens allow the Narcomoeba to enter the Battlefield and, without passing priority, cast Cabal Therapy. The Narcomoeba will be safely back in your graveyard before your opponent can respond. Note that if Emrakul comes up with the Narcomoeba ability on the stack, you can let Emrakul shuffle it back in your library to essentially cancel the trigger. You are probably naming Swords to Plowshares. If any of your Narcomoebas are exiled you have to go back to the search stage and get the Blasting Station in your hand and hardcast it. Now that you have seen your opponent's hand you can use the second Cabal Therapy in this same way to nab Stifle or Path to Exile. There really aren't any other cards to be concerned with. If the opponent has nothing pertinent from the first Therapy, you can use the others to discard combo pieces from your own hand if you are holding any.
Once these details are in order it is safe to let the three Narcomoebas enter the battlefield. Then you are looking to get Sharuum, Dread Return, and Blasting Station in your grave yard before revealing Emrakul. This may take several times through the deck but it must be exactly this way. Once you get this, Dread Return Sharuum who brings in the the Blasting Station. When Blasting Station enters the battlefield you are in business. Just continue to bring the Narcomoebas into play one at a time and sacrifice them to the Station as you do. You will do infinite amounts of artifact damage to any legal target including your opponent.
Some notes:
Triggers and priority are a big part of playing this deck properly. If you do it right, you can remove any chance the opponent has of preventing the combo with graveyard hate and creature removal. That leaves, in order of effectiveness...
Extirpate (must be discarded)
Leyline of the Void (must be bounced)
Wheel of Sun and Moon (must be bounced)
Pithing Needle/Phyrexian Revoker (must be removed)
Gaddock Teeg (must be removed)
Runed Halo (must be removed)
Chalice of the Void, Trinisphere (not hosers, but pretty good on turn 1)
Krosan Grip, Qasali Pridemage, etc (delays the combo)
counterspells (delays the combo)