Hi, I'm Gami and this is my Pioneer Soulflayer list! If you want to play a graveyard combo deck that isn't Greasefang, you're in the right place!
This deck is built to maximise the power of Soulflayer and Urborg Scavengers to apply early pressure with a hard to remove threat.

Deck Info:

Noteable Inclusions:

Gifted Aetherborn - Blocking vs aggressive decks and/or forcing opponents to trade into it is very strong, especially when we don't mind if it dies. Makes the aggro matchups better game one. May become less relevant if you decide to swing the deck to play more aggro hate mainboard, but in this current version is invaluable.

Ledger Shredder - Shredder can block vs aggo and get damage in against control all while forcing our opponents to think about their spells and furthering or gameplan. A worthy four of in the deck.

Samut, Voice of Dissent - This deck is less all-in on Soulflayer than most, only having six main exile targets. Zetapla is fairly standard, Samut less so. The reason why, is that almost any combination of Samut and another creature, is fairly powerful, where other options needed two or three different creatures to have been milled to be a real threat. This means we can run fewer threats overall and have much higher card quality.

Noteable Exclusions:

Cragplate Baloth - Hexproof and haste is fine, but only really good as the first Urborg Scavengers target, even then, Scavengers can still be removed in response.

Adult Gold Dragon - A similar story, extra lifelink is good, but I don't think it's better than Samut. Losing the ability to hardcast it over something like the Aetherborns also isn't ideal, when the reason you'd want more lifelink is more aggro in the meta, so early blockers are key.

Neoform / Atraxa, Grand Unifier - There's an argument that the Atraxa Neoform variant is a better deck, but I think with eight copies of our main threat, we can be equally consistent, if not more so, and pose a bigger, harder to remove threat when we do.

Founding the Third Path - I like this card a lot, it's able to colour fix, cast two spells in one for Ledger Shredder and reuse spells from the graveyard, a lot of what the deck wants to do. But there's one issue, we want to do as much as we can at instant speed, to be able to hold up countermagic and removal when it matters most, so this being a non-creature sorcery speed spell isn't where we want to be in this deck.

Lands - Eighteen is low, but when the most expensive card we're actually trying to cast in the deck is Urborg Scavengers at three mana and we have eighteen ways to filter and draw cards, the deck runs well. Average mana value is 1.7 if we take into account the mana we intend to pay for each card.
Using Frank Karsten's fairly well respected method for calculating the number of lands needed in a deck, that being 19.59 + (1.90 * average cmc) – (0.28 * cheap card advantage spells), we get 19.59 + (1.90 * 1.7) – (0.28 * 18) = 17.78. So the numbers back the experience I've had testing.

Currently Testing:

Urborg Scavengers - With a hasty creature to exile from the graveyard, this can attack the turn it comes down as a 4/4 with keywords, feels very strong.
Savage Summoning - Improves matches against heavy control decks like Azorius and Dimir.
Witch's Vengeance - A one sided boardwipe for three mana seems fantastic against aggressive decks.

Sideboard Theory:

> Rakdos Midrange:

Their Problem Cards:

Go Blank - Exiles graveyards, importantly sorcery speed.
Extinction Event - Kills any Soulflayer setup.
Liliana of the Veil - Can force us to sacrifice a Soulflayer, bypassing all our protection.
Unlicensed Hearse - Exiles graveyards at instant speed repeatably.

Game One:

Favoured for us, their only relevant interaction mainboard is Graveyard Trespasser and Bloodtithe Harvester. Both are only at sorcery speed, so can be played around pretty easily.

Post-Board:

A little harder as any number of Extinction Event, Unlicensed Hearse, Liliana of the Veil, Sheoldred's Edict, Go Blank and Necromentia come in. These all get countered by Stubborn Denial luckily and it doesn't feel too bad to keep the Denials in as Fable of the Mirror-Breaker or Thoughtseize can also be hit early game before Ferocious is online.

Changes:

In:
3x Abrupt Decay - Hitting a resolved threat is still necessary.

Out:
2x Tainted Indulgence - Slowest dig option, need to be more efficient against this style of deck.
1x Samut, Voice of Dissent - No hexproof or indestructible makes her a little win more here, the game will most likely be longer, so cutting one mill target doesn't feel too bad.

> Nykthos Ramp:

Their Problem Cards:

Karn, the Great Creator - Access to sideboard and silver bullets game 1.
Storm the Festival - Generates a lot of advantage that is difficult to come back from.
Nykthos, Shrine to Nyx - Nykthos is manageable as long as we can keep devotion off the board and answer whatever they play.
Kiora, Behemoth Beckoner - Untaps Nykthos and generates tons of mana.

Game One:

Tough, but winnable. If they get a good hand, we have to disrupt early or we lose, if they get a normal hand and we disrupt early, it's likely we win.
Keep them off high devotion if you can, don't focus desperately hard on getting a max-power Soulflayer, anything that fights a Cavalier and lives is good enough.
Gifted Aetherborn and Ledger Shredders really help in applying pressure while furthering our gameplan.

Post-Board:

Slightly better, but still not great. Nykthos almost never sideboards, making Game 2-3 almost objectively better for us.
Assasin's Trophy is mostly there to disrupt their combo, hitting any Planeswalker or Nykthos itself. Can kill a Cavalier in a pinch if we need to push damage through.

Changes:

In:
3x Abrupt Decay - Removes creature devotion or Kiora, good for keeping them on their combat plan.
2x Assassin's Trophy - Kills bigger threats like Karn and Cavalier, can even hit Nykthos.

Out:
2x Striped Riverwinder - Hexproof is less important against a deck with low removal. Cycling is still nice though.
2x Tainted Indulgence - Worst two mana dig option in this matchup, need to fill the graveyard faster and dig harder than this allows.
1x Stubborn Denial - Nice to catch a planeswalker or Storm the Festival, but otherwise, mostly dead.

> Azorius Control:

Their Problem Cards:

Farewell - Exiles any Soulflayer setup.
Rest in Peace - Shuts down our entire gameplan
Absorb / Make Disappear - Counters our creatures, worst with Soulflayer who delves as a cost.

Game One:

Do not overextend, they have quite a few blowout cards, take your time, don't rush. Force them to boardwipe smaller threats like Shredders or Aetherborns, cast instants when they tap out at end step. This is not a race.
Don't be afraid to cast Urborg Scavengers early with no value, if you think you can get them to resolve and start getting damage in, do. If you can start exiling relevant things as well, even better.

Post-Board:

Rest in Peace absolutely destroys our gameplan, so try to always have removal or counters for it. Other than that, very similar to Game One, just with the addition of being able to flash in Soulflayer occasionally to catch them off guard.

Changes:

In:
2x Spell Pierce - Interacting early is key here, hitting RiP or resolving something through a counterspell is great.
2x Assassin's Trophy - Hits RiP and all their planeswalkers.
1x Savage Summoning - Making a Soulflayer uncounterable and flash speed is incredibly good.

Out:
3x Gifted Aetherborn - Lifelink doesn't help here and they're not going to beat down on their own.
2x Tainted Indulgence - Trimmed the slowest dig card to fit in sideboard protection.

> Lotus Combo:

Their Problem Cards:

Lotus Field - Gives them the mana to win fast.
Emergent Ultimatum - Tutors for their combo
Languish - Kills any Soulflayer setup.

Game One:

This is why the Stubborn Denials are mainboard, counter their spells, Thoughtsieze their hand, apply pressure as fast as possible.

Post-Board:

Slightly better, as we have fewer dead cards, but the same still applies. Disruption and pressure wins games here.

Changes:

In:
2x Spell Pierce - Lots of good targets in the deck.
2x Assassin's Trophy - If they bring in big creatures like Dragonlord Dromoka or Zacama, Primal Calamity, it's good to have at least one answer. Hitting a Thespian's Stage in response to them copying a Lotus is also good.

Out:
3x Gifted Aetherborn - Deathtouch and lifelink don't help here, it could be argued that chip damage with a 2/3 is relevant, but playing something that does nothing to stop their gameplan, or further ours is an easy cut.
1x Striped Riverwinder - Some versions of Lotus play Fading Hope, but I think the risk is small enough that we can cut back one Riverwinder.

>Abzan Greasefang:

Their Problem Cards:

Greasefang, Okiba Boss - Reanimates and crews vehicles.
Parhelion II - Cheated into play.
Liliana of the Veil - Can force us to sacrifice a Soulflayer, bypassing all our protection.

Game One:

Getting a strong Soulflayer is borderline game over. Both decks combo at similar speeds, but we have eight threats and they only have four, some are running six if you count Eldritch Evolution or Traverse the Ulvenwald.

Post-Board:

They have more removal sideboard, with Liliana of the Veil and Vanishing Verse, so now the requirement for an immoveable Soulflayer is hexproof, indestructible and to have one other creature on board. Matchup feels in our favour.

Changes:

In:
4x Ray of Enfeeblement - Kills Greasefang
2x Assassin's Trophy - Will remove any graveyard hate or game winning threat.

Out:
3x Stubborn Denial - Greasefang is the focus, non-creature counters come out.
2x Tainted Indulgence - Doesn't fill the graveyard as fast as we need.
1x Ledger Shredder - With their ability to combo at any time, holding up mana becomes more important, cutting back very slightly on the sorcery speed.

> Dimir Rogues:

Their Problem Cards:

Sheoldred's Edict - Will kill a Soulflayer if we have no other creatures to sacrifice.
Drown in the Loch - Fairly easily turned on by our self mill, hard counter.

Game One:

Outside of an edict, they cannot beat a strong Soulflayer. Early pressure is key, we can go over the top of them, but have to make sure the gates are down before they get going.

Post-Board:

They don't have a huge amount to bring in against us, which is beneficial, Into the Story and Cling to Dust are fine against us, but mostly ineffective, gameplan stays very similar to game one, just with better sideboard options from us.

Changes:

In:
2x Abrupt Decay - Will get rid of anything apart from Sheoldred.
1x Witch's Vengeance - Three mana one-sided wipe.
1x Ritual of Soot - Worse than Vengeance, but will still tilt the match in our favour.

Out:
4x Thoughtseize - Not worth the life loss against an aggro deck.

> Temur / Izzet Creativity

Their Problem Cards:

Indomitable Creativity - Main path to them winning the game
Make Disappear - Hits creatures, can't be stopped by a single counterspell if they cast it with Casualty.
Divide by Zero - Counterspell or bounce spell, makes hexproof important.

Game One:

Temur needs to get to five mana and two tokens to flip into Worldspine Wurm and Xenagos, God of Revels to one-shot the opponent. Izzet only needs four and one, but their payoff is much less impactful.
Soulflayer and Creativity combo at similar speeds, but Creativity has much more vulnerable points of interaction, they also only have four copies of Creativity, where we have eight of our main threat.
The plan game one is simply to resolve a Soulflayer, doesn't have to be particularly strong, hexproof + lifelink / doublestrike will do. Once we have pressure, hold up mana and counter any attempts to cast Indomitable Creativity.

Post-Board:

After boarding it's quite similar. Take your time and be ready for a fight on the stack.

Changes:

In:
2x Spell Pierce - More disruption early
2x Assassin's Trophy - If they do manage to resolve an Indomitable Creativity or hardcast a Shark Typhoon, this can get us back in the game.

Out:
3x Gifted Aetherborn - Deathtouch and lifelink don't help here, it could be argued that chip damage with a 2/3 is relevant, but playing something that does nothing to stop their gameplan, or further ours is an easy cut.
1x Ledger Shredder - They will have a lot of dead removal spells, so creatures aren't the way to go here, trimmed one.

>Mono-White Humans:

Their Problem Cards:

Brutal Cathar - Exiles a non-hexproof Soulflayer. Even if we get it back, it loses the keywords.
Rest in Peace - Shuts down our Soulflayer gameplan.
Thalia, Guardian of Thraben - as a low curve deck with few lands, adding 30-50%+ to the cost of our spells hurts.

Game One:

Has the potential to be one of our worst matchups, I decided to gear the maindeck towards combo more and the sideboard towards aggro, you might prefer it the other way around, mostly a meta call.
Will be difficult to win this one unless you run pretty well on your mill and draw. They can't beat a full Soulflayer setup, but they will not give little time to get there. Prioritize lifelink, hexproof and blockers first. hope to close the gates before they kill us.

Post-Board:

Quite a bit better with seven sideboard cards in. Same as game one, prioritize lifelink and hexproof to make an impossible to remove Soulflayer as soon as possible.

Changes:

In:
4x Ray of Enfeeblement - Hits every creature in the deck
3x Abrupt Decay - Hits almost every creature and Rest in Peace.
1x Witch's Vengeance - Three mana to not lose if they get a good draw.
1x Ritual of Soot - If they get too big for Witch's Vengeance to kill.

Out:
4x Thoughtseize - Hand interaction is much less important in the aggro matchup.
3x Stubborn Denial - No noncreature spells outside of RiP and Brave the Elements, much less useful here.
2x Tainted Indulgence - Needing to be much more removal heavy, cut some of the slower draw.

>Spirits (Mono-Blue / Azorius / Bant):

Their Problem Cards:

Lofty Denial - Easily counters a Soulflayer
Geistlight Snare - Easily counters a Soulflayer
Rest in Peace - Shuts down our Soulflayer gameplan.

Game One:

As with most aggro decks, they can't beat a resolved Soulflayer with good keywords, they offer less pressure than other aggro decks, but more disruption.
Game one should be relatively straightforward, block with Ledger Shredders, resolve a Soulflayer when you can, win from there.

Post-Board:

Mostly the same, apart from the threat of turn two Rest in Peace, if this happens we can block with Shredders and gain life back with Aetherborn, but we really need to find Abrupt Decay to get out of the lock.

Changes:

In:
2x Spell Pierce - A surprisingly high number of counters we need to be ready for.
1x Witch's Vengeance - Three mana one-sided wipe.
(3x Abrupt Decay - If they're in the colours for Rest in Peace, these come in.)

Out:
3x Thoughtsieze - Not enough counters for us to have to Thoughtsieze aggressively, not having to take the life loss is also nice.
(2x Tainted Indulgence, 1x Thoughtseize - Makes space for the Abrupt Decays, least relevant cards in the matchup.)

>Mono Red Aggro:

Their Problem Cards:

Wizard's Lightning - Kills both of our two drop x/3s
Kari Zev's Expertise - Can steal a Soulflayer without a full setup.
Rampaging Ferocidons - Stops our lifegain if we have it.

Game One:

They will be fast, but have literally no way to remove a resolved Soulflayer, if we get indestructible and lifelink, it's basically game over.

Post-Board:

They can bring in Rampaging Ferocidons to stop us gaining life, but even so, eight damage a turn is hard to race, especially if they're losing attackers attacking into a Soulflayer with vigilance.

Changes:

In:
2x Abrupt Decay - Removes any of their creatures.
1x Witch's Vengeance - Three mana one-sided wipe.
1x Ritual of Soot - Worse than Vengeance, but will still tilt the match in our favour.

Out:
4x Thoughtsieze - Nothing worth taking, especially not at the cost of two life.

Not updated

> Gruul Boat:

Their Problem Cards:
Skysovereign, Consul Flagship - Very evasive to all of our removal as it'll most likely only be a creature on their turn. Needs a Zetalpa Soulflayer to get through it.
The Akroan War - Will steal a non-hexproof Soulflayer for multiple turns.

In:
3x Assassin's Trophy - At the cost of a basic land, kills any threat, the panic button.
2x Abrupt Decay - Destroys every creature in the deck.

Out:
3x Fatal Push - Only hits elves and the occasional token.
2x Thoughtseize - Unless I'm discarding an Akroan War or Skysovereign, this isn't worth it here.

> Selesnya Angels:

Their Problem Cards:
All the angels have flying, so our usual evasion won't be as good.
Deafening Silence - This isn't as bad as it looks as we can play a lot at instant speed, removed fairly easily by Abrupt Decay if it gets too taxing.
Shapers' Sanctuary - To slow them down enough to set up Soulflayer, we're going to need to remove their creatures, Sanctuary gaining them a card each time we do is pretty bad.

In:
4x Abrupt Decay - Removes every non-land permanent in their deck, always a good card to have in hand.

Out:
2x Striped Riverwinder - They have no removal that hits a 4BB creature, so hexproof isn't needed in the Soulflayer pile, cycling is still nice though.
2x Thoughtseize - Discarding a Collected Company is nice, but they're a pretty resilient deck.

>Izzet Phoenix:

Their Problem Cards:
Thing in the Ice - Can force us to return a Soulflayer to our hand if it flips.
Disdainful Stroke - Counters our Soulflayer.

In:
3x Stubborn Denial - This matchup will be fought on the stack.

Out:
2x Thoughtseize - They have large redundancies and plenty of draw, discarding Phoenixs is essentially beneficial.
1x Cragplate Baloth - Hexproof isn't needed here.

>Five-Colour Fires:

Their Problem Cards:
Fires of Invention - The engine of the deck.
Disdainful Stroke - Counters our Soulflayer.
Rest in Peace - Shuts down our entire gameplan.
Various targeted exile effects - Need Hexproof.

In:
3x Assassin's Trophy - Kills the bigger threats if they have time to stabilise.
2x Abrupt Decay - Removes their early enchantments, notably RIP.
1x Haywire Mite - Can be searched with Fauna Shaman, hits all their important enchantments.

Out:
4x Fatal Push - Not a small creature based matchup.
2x Ledger Shredder - If they're casting two spells a turn, we're probably losing.