Basically the point of this deck is to Surgical Extraction our own Shadowborn Apostle, which lets us remove almost all of our deck. This makes Shelldock Isle very useful, since we can then grab an Emrakul, the Aeons Torn and proceed to win. The easiest way to do this is to be on the draw, then simply draw and discard a Shadowborn Apostle. You will have one, in all of my playtesting I've never had less than one in my hand.

The Card Choices:

Shadowborn Apostle: Better than Relentless Rats, mainly since we can chump block with them with only one land. They also have a secondary mode if really necessary.

Surgical Extraction: Our combo enabler. Feel free to use it on Surgical Extraction after comboing off, this way we have a higher chance of getting an Emrakul out.

Shelldock Isle: Our way to cast Emrakul. After exiling 2/3rds of our deck, we can find another Isle or an Emrakul. Then cast it and let the fun begin.

Emrakul, the Aeons Torn: Our primary win condition. A flying spaghetti monster on turn 3, and we get the cast trigger? I think we win that game.

Rune-Scarred Demon: Our last hope if we ended up with no Surgical Extractions. Play 6 apostles, fetch him, fetch Surgical Extraction, proceed to win.

Serum Powder: The only other card that makes the cut. It lets us keep ourselves at 7 cards in hand while mulliganing, which is very important to our "draw, discard" gameplan. Totally useless once we start playing the game.

Sample Ideal Hand

T1: Draw, discarding a Shadowborn Apostle at end of turn. On their turn, use Surgical Extraction to exile all Shadowborn Apostles from your library.

T2: Shelldock Isle, hiding an Emrakul, the Aeons Torn underneath. If you want this to be super ideal, we would Surgical Extraction our Surgical Extraction first to increase our odds.

T3: Play Watery Grave or Darkslick Shores, use Shelldock Isle to cast Emrakul, the Aeons Torn. Laugh manically as they lose to the flying spaghetti monster.

Sample "Oh Damn, I Have No Extraction" hand

T1: Land, Shadowborn Apostle

T2: Land, 2x Shadowborn Apostle

T3: 2x Shadowborn Apostle (It's highly unlikely that we will get a third land)

T4: Shadowborn Apostle, crack all 6 for a Rune-Scarred Demon, fetching Surgical Extraction, casting it on Shadowborn Apostle.

T5: Go to T2 of the Ideal Hand section.

Sideboarding

Extirpate: This helps our control matchups. It will slow us down by a turn, but it also guarantees that we get the finding effect. WARNING! Extirpate will remove the Shadowborn Apostles from your hand as well as your library. Expect no chump blockers. You can cut either Serum Powder or some Shadowborn Apostles for these.

The Demon Plan/Thrumming Stone combo

This is what we play against a deck with a lot of hand disruption, like 8rack, where we know our combo won't be going off. This would be a game 3 option mainly, after we see what they have sided in.

We side out 4x Emrakul, the Aeons Torn, 4x Serum Powder, and 3x Surgical Extraction.

We then side in the rest of our sideboard.

Rune-Scarred Demon: This lets us find a Thrumming Stone to combo. Adds consistency, and we have 2 to ensure we don't die if we draw one.

Griselbrand: For the aggro matchups. He lets us gain life to tide us over, and the "Draw seven cards" section is really handy.

Thrumming Stone: This is the new combo we will use. You play it on turn 5, then cast a Shadowborn Apostle. You then proceed to flip your deck, putting every Shadowborn Apostle out of it onto the battlefield. From there, you can simply swing with your 25-30 apostles and win.

Immortal Servitude: You got board wiped after comboing? Just spend four mana and get them all back!

Swamp: We need mana, and this is the best way to do it. I was tempted to use Mana Confluence so you can also activate Shelldock Isle after comboing with Thrumming Stone, but it seems less relevant.