This is a graveyard-based combo deck that aims to fill the graveyard with spells like Otherworldly Gaze, Contingency Plan, and Taigam's Scheming, before casting a 6-cmc delve creature like Hooting Mandrills or Tasigur, the Golden Fang and using Neoform or Eldritch Evolution to sacrifice it and get Atraxa, Grand Unifier onto the battlefield as early as turn 3.
We should be aiming to execute our combo on turn 3 or 4 in most matchups. Turn 3 is the fastest possible combo (with the exception of your opponent interacting with you, which can allow a turn 2 Atraxa), and the deck is pretty consistent at finding it. Any of the 12 self-mill spells + delve creature + Neoform is a t3 Atraxa. The self mill spells can also find you your missing piece for the next turn, whether thats a creature, neoform effect, or a third land. Self-mill spell + Tasigur, the Golden Fang + Mox Amber + Eldritch Evolution and Otherworldly Gaze + 2nd Gaze/Thoughtseize + delve creature + Eldritch Evolution are also t3 combos.
The main target for cheating into play is Atraxa, Grand Unifier since she has crazy value on her etb ability and is has a big body that stabilizes our life total while also being a three-turn clock. Even if she gets removed, she usually allows us to find the right cards to simply combo again and get another Atraxa down the line. Titan of Industry is the only other maindeck target for when we want to cheat in a second creature or if our opponent used a Necromentia type effect to remove our Atraxas. Essence Flux is another important payoff for our combo which usually simultaneously blanks a removal spell while generating a ton of card advantage. We can frequently find an Essence Flux off an Atraxa trigger, and use it to flicker Atraxa to find a second copy, etc.
In the sideboard, we have Chaos Maw and Dragonlord Atarka as additional targets against creature-based aggro decks, and Hullbreaker Horror for control decks. An Essence Flux-ed Chaos Maw will usually wipe our opponent's entire board.
Mox Amber is a pretty techy card that works surprisingly well in the deck. With Tasigur, the Golden Fang in play, it allows us to execute the combo t3 with protection in the form of Stubborn Denial, Thoughtseize, or Duress. It's another card type we can find off Atraxa, and if we find Mox Amber + Essence Flux off Atraxa we can hold up protection from a removal spell and get another etb trigger.
In terms of resiliency, the deck is a bit tougher than one might think. As a graveyard-based combo deck, graveyard hate will obviously set us back. However, we usually only really care about replacement effects like Rest in Peace and Leyline of the Void. One time exile effects like Tormod's Crypt and Go Blank set us back, but are pretty easily to recover from. Effects like Grafdigger's Cage and Weathered Runestone do absolutely nothing. Ashiok, Dream Render is one exception as an exile effect that also prevents us from searching our library, but since it is a 3 drop we can beat it on the play, or discard/counter it on the draw. Given the current state of the pioneer meta, graveyard-based decks are not super popular so Leyline of the Void in sideboards is pretty rare, which is why I am not running any answers like Assassin's Trophy or Stern Dismissal. For Rest in Peace, we have 12 answers across the main and side: 4 Thoughtseize, 2 Duress, 2 Abrupt Decay, and 4 Stubborn Denial.
Spot removal is also not a big deal for us, since we can hold priority after casting a delve creature to immediately cast a Neoform effect, and the sacrificing is part of the spells cost. We have Essence Flux to blank removal, and even if they successfully remove an Atraxa we probably have enough cards in hand to just do it again. To deal with countermagic and discard effects, we can use our own countermagic and discard effects. For Necromentia effects, we have multiple targets in both the main and side, and a lot of redundancy in our combo (2 delve creatures, 2 evo effects, 3 self mill effects). And lastly we can occasionally switch to a delve creature beatdown plan, as it's possible to get 2 delve creatures on the battlefield by turn 3 (8 power), or 12 power on the board by turn 4.
