Let me set up a perfect handYou will need 2 Dark Ritual, 1 Shadowborn Apostle, 1 Thrumming Stone, 1 Shirei, Shizo's Caretaker, 1 Swamp, and 1 Nykthos, Shrine to Nyx.
Turn one you play a Swamp. Tap the Swamp to play a Dark Ritual. Use one of the black mana produced by Dark Ritual to cast another one. You will now have five black mana in your mana pool. Use this to cast Thrumming Stone.
Turn two, you will play Nykthos, Shrine to Nyx and a Shadowborn Apostle. The Shadowborn Apostle will have the effect Ripple 4, which allows you to look at the top four cards of your library and put any number of them onto the battlefield if they share the name with the card cast. This will allow you to go through your whole library (In a typical game) because the deck runs 22 Shadowborn Apostle, so you will end up with all 22 of them on the battlefield.
Turn three, you will hopefully have drawn another Swamp by now. If you have, play it, tap both of your swamps to activate the ability of Nykthos, Shrine to Nyx. This will add 22 black mana to your mana pool. Use that mana to cast your Shirei, Shizo's Caretaker. Hopefully, you will have also drawn a Xathrid Necromancer by now as well. If you have, cast it. Next, activate the ability of Shadowborn Apostle to sacrifice six of them to search your library for Abhorrent Overlord. Because you played Shirei, Shizo's Caretaker, all six of your Shadowborn Apostles will be returned to the battlefield, and your Xathrid Necromancer will give you a 2/2 black zombie for each human that dies. Since Shadowborn Apostle is a human, you will get 6 2/2 black zombies for every time you activate the ability. When your Abhorrent Overlord enters the battlefield, you will have a devotion to black equal to 26. This will get you 26 1/1 Harpy's with Flying. Activate the ability of Shadowborn Apostle again to get a second Abhorrent Overlord. This one will get you another 28 1/1 Flying Harpy's. The third and fourth Abhorrent Overlords will get you 30 and 32 Harpy's respectively. This gives you a total of 116 1/1 Harpy's with Flying, and also 24 2/2 black zombies. You will still have all 22 of your Shadowborn Apostles as well.
Turn four, if you draw into a Zulaport Cutthroat, activate the ability of Nykthos, Shrine to Nyx and then play Zulaport Cutthroat. You will still have 30 black mana in your mana pool that you can use to sacrifice 6 apostles at a time for 30 times with no target. This will deal 180 damage to each of your opponents, you will gain 180 life, and you will get 180 more 2/2 black zombies.
This is a perfect game for this deck as it currently is. I am sure that it can be improved, so I am eager to hear your suggestions. If you have questions about this, or think of something that can make this better, please let me know.
