Whispers of the Delirium Brood
This is an Midrange-Control deck that aims to disrupt your opponent's plan and then kill them with efficient creatures. The deck uses Sultai-colored/Delirium cards to improve your match-ups against combo/big mana decks and other grindy decks over similar archetypes like Jund and Abzan. The deck is basically a pile of individually powerful cards, 8 cantrips, and Whispers of Emrakul.
Main Deck Rationale
Feature Cards
Whispers of Emrakul: Let's start with the elephant in the room. a) No you don't always have delirium on turn 2. b) You usually have delirium by turn 3 or 4 - and Affinity is the only deck that consistently empties their hand by turn 4. c) If something goes wrong with getting delirium you can discard it to Liliana of the Veil or Collective Brutality. d) The Hymn to Tourach version has been awesome every single time I've cast it. e) It has won me multiple games on it's own.
Traverse the Ulvenwald: This card is totally insano. It's synergy with Snapcaster Mage makes it so hard for anyone to grind against you. You can maindeck tutor for Shriekmaw, and then in the sideboard you have great bullets for slower match-ups.
Disruption
Inquisition of Kozilek + Thoughtseize: Thoughtseize is theoretically better than Inquisition of Kozilek in this deck but you do a pretty high amount of damage to yourself with your manabase so Inq gets the higher number. This concern for your life total is one disadvantage over Death's Shadow variants. Still, the 2 work beautifully with Snapcaster Mage.
Collective Brutality: I started maindecking this card as a concession to Burn and it's been fine. It's quite good against combo decks and Collected Company. Still, don't hesitate to board it out.
Fatal Push: Everyone knows this card is great, it's just worth stating that it's particularly easy to trigger revolt in this deck because of Mishra's Bauble.
Abrupt Decay: God I love this card. Sultai has such good answers to every type of permanent (but lands) and Abrupt Decay is a major reason for that. Main deck enchantment removal is great because it helps you achieve the mighty 7/8 Tarmogoyf.
Shriekmaw: It's a removal spell you can tutor for. It also really helps you turn on Delirium for turn 3 and is a great later game 2 for 1. The card has been 2x in my deck sometimes and is generally fantastic (except against Affinity).
Liliana of the Veil: She's the best card in modern and all of her modes complement the deck. She'd be 4x but you cantrip so much that I haven't found it necessary. Liliana, the Last Hope works great with Delirium but is just so much less generically powerful that I moved her out of the 75 completely.
Threats
Tarmogoyf: The big bag Lurgoyf is usually a 5/6 in this deck thanks to Mishra's Bauble and Thoughtscour. Dying to Fatal Push sucks but having a bigger butt than Tasigur, the Golden Fang and Reality Smasher does not suck.
Grim Flayer: This card's real value is against combo/less interactive decks because he's great at helping you continue to find answers while you kill them. He's incredibly strong against burn for this reason.
Tasigur, the Golden Fang: This is essentially a 1 mana 4/5 for which you can tutor, which is awesome. You put such an incredible amount of cards in your graveyard that you rarely turn off Delirium or power down Tarmogoyf.
Utility Spells
Snapcaster Mage: He's totally bonkers in this deck because of Traverse the Ulvenwald.
Mishra's Bauble + Thoughtscour: These guys turn on Delirium, buff Tarmogoyf, and let you run only 17 lands.
Sideboard Rationale
My overall conclusion with sideboarding for this deck is that you should not count on Traverse the Ulvenwald targets against decks that you can't effectively slow down with your disruption package (e.g. burn and affinity).
Tutor Targets
The Scarab God: I don't think grinding is a good strategy to beat this deck, but some decks are stuck on that plan. If they are, they mostly cannot beat The Scarab God. Every time I've cast him I've proceeded to utterly destroy my opponent. My favorite is to reanimate a Snapcaster Mage and flashback Traverse the Ulvenwald.
Reclamation Sage: He's fantastic in tons of match-ups. Between him, Abrupt Decay and Maelstrom Pulse you have a lot of ways to deal with artifacts and enchantments.
Vendilion Clique + Mystic Snake: These both come in against decks like Titan Shift, Eldrazi Tron, Ad Nas, etc. Basically any deck you can slow down but need extra time to kill them.
No Time to Tutor Targets
Ceremonious Rejection: Yay 1 mana counterspells and boo Tron. I'm not completely sold on this card yet.
Collective Brutality: I tried all sorts of tutor targets against burn and they're all too slow. The utility against combo deck is nice too.
Damnation: I found this to generally be better than Flaying Tendrils and you have so much spot removal that it becomes very useful against affinity.
Disdainful Stroke: This card is excellent in the meta right now. I've done well against Titan Shift using the combo of this, hand disruption, Vendilion Clique, and Mystic Snake. It helps that Whispers of Emrakul is pretty bonkers against them of course...
Leyline of the Void: I tried lots of tutorable graveyard hate targets and none of them were going to give you a fighting chance against Dredge or Living End, so here we are. The splash damage against Death's Shadow is nice but that match-up is quite winnable without this.
Maelstrom Pulse: I'm saving the best for last; having catch all answers like this is incredible.
