This Standard Bo1 deck uses Peer into the Abyss to dump all of your combo pieces into the graveyard and Eerie Ultimatum next turn to drain for lethal.

The main reanimation targets are Scute Swarm, Vito, Thorn of the Dusk Rose, and Kor Celebrant. Bringing these out all at once with several lands will cause the scutes to multiply, stacking loads of celebrant triggers, and draining the opponent for lethal with Vito. We run three of each of these along with Eerie Ultimatum to make drawing them with Peer as consistent as possible without overloading our slots.

Secondary reanimation combo pieces are Selfless Savior which protect your reanimated creatures from instant-speed destruction, and Lotus Cobra which allows you to easily chain two or more Eerie Ultimatums that turn. You can respond to your opponent's spells by cracking Fabled Passage and/or Evolving Wilds to force triggers before resolution. Lastly, paying 3 to put Yorion into your hand allows you to dump it with Peer into the Abyss for even more ETB trigger drain. All of these factors make the combo nearly impossible to stop the turn it goes off.

One of the powerful synergies in this deck is with Shatter the Sky/Extinction Event, and Once and Future, which lets you repeatedly blast off board wipes starting on turn four. Because Once and Future is an instant, you can hold up mana to cast it at the end of your opponent's turn. People tend to assume it's safe to go wide the turn after a board wipe, and with this, you can easily catch them off-guard.

The general strategy is to disrupt your opponent and take care of anything that cannot be chump-blocked so that you can survive the turn after Peer into the Abyss.

Selfless Savior lets you protect your Cobra from removal, keeping your early ramp consistent, or allow one of your creatures to survive a Shatter the Sky (Greathorn, Scute, Yorion) and continue beating them down. If your combo doesn't go off, you can generally win using your creatures to pummel your opponents and Vito to help extend your damage. Kor Celebrant, Vito, and Migratory Greathorn give you the toughness to keep opponent's creatures from getting through when you aren't repeatedly blowing up the board. 

Migratory Greathorn is a key component of this deck and has been chosen over Cultivate for the number of benefits it brings. First and foremost, It's a ramp effect that comes stapled onto a body that deters anything 3/3 or lower from attacking and can chump both Brushfire Elemental and Questing Beast, leaving them open to be hit with a board wipe next turn. Aside from comboing with Scute Swarm to clone Greathorns, you can get a lot of value out of the 3/4 body just by hardcasting it on-curve. There are a lot of different strategies you can employ with this card, being sure to consider them can help you swing the game in your favor.

Yorion can do a few tricks aside from filling out otherwise dead turn 3s. The deck isn't as hard-focused on blinking syngergies with him, so he isn't included in the mainboard, but you can often find yourself getting 4+ life drains when you cast him, or at least staving off fliers long enough to answer them. Don't forget you can use him to split up Migratory Greathorn stacks.

Tyramet Calls the Dead helps fill your graveyard as a contingency plan for if you're in a spot where you don't have or can't afford to Peer before casting Eerie, as well as providing blockers, life gain, and scry for fishing out your game-enders. Blinking this saga helps you dig deeper and gives you an opportunity to drain 4 with Vito.

Elspeth's Nightmare is too good of a card to leave out, dealing with small creatures but particularly those that become large threats (Thieves' Guild Enforcer, Brushfire Elemental.) The discard gives you a chance to get rid of noncreature permanents, and the graveyard exile takes the gas out of decks like Lurrus and Kroxa.

I originally split the 3 creature combo pieces with Daxos/Impassioned Orator, Maurading Blight-Priest, and Felidar Retreat so that you can pull multiples out with Eerie, but found that the higher toughness was too important early game, and that Felidar Retreat usually ends up as a win-more when your combo goes off, while not pulling enough weight with an empty board. Scute on the other hand allows you to quickly run away with the game via life gain and/or life drain with just Vito or Celebrant on the field, or Migratory Greathorn in hand. Especially with smaller Ultimatums that pull out fetch lands.

The best strategy for fetching lands here is to first fetch two white sources, and then fetch nothing but black. You want to be able to cast Shatter the Skies if you topdeck it turn 4. And three black ensures you can still cast Peer into the Abyss if the rest of your mana happens to not line up with Eerie Ultimatum.

This deck has notably won games against Mono-Green Food, Gruul Landfall, Rakdos Control, Boros Cycling, and Lurrus Rogues, with earlier iterations beating Esper Yorion and Rakdos Midrange. This deck has performed very well without Castle Locthwain, but consider swapping out one or two Swamps for it.