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:

Vampire of the Dire Moon / Banehound - 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 how many spells they're casting and furthering or gameplan. A worthy four of in the deck.

Samut, Voice of Dissent - This deck is less all-in on creatures for Soulflayer to delve 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 three to four different creatures to have been milled to be a real threat without Zetalpa. 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, Vampire of the Dire Moon or Banehound 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 we can be equally consistent, if not more so, and pose a bigger, harder to remove threat, even if it doesn't refill our hand.

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 20 ways to filter and draw cards at two mana or less, the deck runs well. Two land hands are perfectly keepable if they have 1-2 dig spells.
The average mana value of the maindeck is 1.56. If we take into account the mana we actually intend to pay for each card. Using Frank Karsten's fairly well respected method for calculating the minimum 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 * 1.53) – (0.28 * 19) = 17.18 lands, so hopefully that gives you some confidence!

>Currently Testing:

Glissa Sunslayer - Alternate pressure against control and destroys grave hate if needed.

Consider - Another one cost dig spell for Ledger Shredder hopefully makes our draws a lot more consistent.

Banehound / Vampire of the Dire Moon - Cheaper than Gifted Aetherborn while hopefully being the same or only slightly worse in most situations.

Rona's Vortex - Versatile bounce with a removal option for more mana.

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 discarded by Thoughtseize and countered by Stubborn Denial.
Be careful if Sacrifice reveals Jegantha, the Wellspring game one but not game two, this means they likely have brought in Lelyline of the Void.

Changes:

In:
2x Abrupt Decay - Hitting a resolved threat is still necessary.
1x Assassin's Trophy - A third Abrupt Decay that also kills Sheoldred.
1x Glissa Sunslayer - Removing Fables and planeswalkers is very useful. Difficult to block, a good source of card advantage while also providing keywords for the Soulflayer pile.

Out:
2x Rona's Vortex - Bouncing back to their hand isn't great when they're likely to be low on resources too.
1x Otherworldly Gaze - While this is good, it doesn't actually draw us a card, trimmed two.
1x Banehound - No deathtouch means that this is a much less thretaning blocker.

> 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 interact early or we lose, if they get a normal hand, interacting early makes it 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.
Vampire of the Dire Moon and Banhound really help in applying pressure as they have to choose between sacrificing a creature to block and lose devotion or let their planeswalkers start taking hits. Glissa also helps with this post-board.

Post-Board:

Slightly better, but still not great. Nykthos almost never sideboards though, making Game 2-3 almost objectively better for us.
Assassin'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:
2x Abrupt Decay - Removes devotion or Kiora, keeps them on their combat plan.
2x Duress - Throwing away a Karn, Kiora, Storm the Festival or whatever other bomb they happen to have in their hand is great for us here, slow them down enough to get out a Soulflayer.
1x Assassin's Trophy - Can hit Karn, Cavalier, Nykthos as well as everything Abrupt Decay hits.
1x Glissa Sunslayer - Can remove their ramp enchantments, kill their planeswalkers and get devotion off the board aif they decide to block.

Out:
2x Ledger Shredder - Blocking won't be much use unless we put 2+ counters on it, attacking won't be much use as Cavalier of Thorns and Polukranos Reborn have reach. Don't want to completely cut our discard outlets though.
2x Striped Riverwinder - Outside of Karn wish targets, they have no way to remove a Soulflayer, and most of their wishboard doesn't deal with it well, going down a few hexproof creatures is safe here.
1x Consider - With fewer Ledger Shredders we need fewer one mana cantrips to connive.
1x Banehound - Lifelink and haste aren't key in this matchup, shaved for more relevant cards.

> 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 Shredders, Vampires and Banehounds, 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 but we have more disruption and they have Rest in Peace.

Changes:

In:
3x Mystical Dispute - Interacting early is key here, hitting RiP or resolving something through an Absorb is great.
2x Duress - For shredding their hand, keeping them low on resources and trying to pick a hole in their defences.
1x Glissa Sunslayer - An additional threat that can kill Planeswalkers, draw cards and remove graveyard hate.

Out:
2x Vampire of the Dire Moon - Lifelink doesn't help here and they're not going to beat down on their own.
2x Otherworldly Gaze - The earlier turns will be spent interacting, so going down some Gazes here feels safe.
1x Banehound - Not enough of a threat and keywords aren't the most useful.
1x Consider - We don't need to be quite as fast against control.

> 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:

Thoughtsieze their hand, apply pressure as fast as possible. We have relatively few ways to deal with their combo mainboard.

Post-Board:

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

Changes:

In:
3x Mystical Dispute - Catches a lot of important spells, most notably Emergent Ultimatum and Pore Over the Pages.
2x Duress - Taking draw / search spells and untap cards leaves them low on resources and buys us time to execute our plan.
1x Assassin's Trophy - If they board in Zacama or other big threats, we want at least one thing that can remove it. Can also hit Thespian's Stage in response to it copying Lotus.

Out:
2x Vampire of the Dire Moon - Deathtouch and lifelink don't help here and it's hard to argue that chip damage with a 1/1 is relevant. Playing something that does nothing to stop their gameplan, or further ours is an easy cut.
2x Striped Riverwinder - Very little removal coming from Lotus so we can get away with less hexproof.
2x Otherworldly Gaze - Against Lotus, cards in hand is key, Gaze not actually drawing us a card isn't where we want to be.

>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 seven threats and they only have four, some are running six if you count Eldritch Evolution or Traverse the Ulvenwald, but these take much more time than the dreaded turn three Greasefang.

Post-Board:

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

Changes:

In:
3x Ray of Enfeeblement - Kills Greasefang.
2x Abrupt Decay - Kills Greasefang and a variety of other things that stop our gameplan like Unlicensed Hearse.
1x Assassin's Trophy - Used mostly as a second copy of Abrupt Decay, but can also hit Leyline of the Void if they have it.

Out:
2x Striped Riverwinder - They have limited removal so most instances of hexproof can come out.
2x Vampire of the Dire Moon - This match will be won with a few big combat steps, not a 1/1 on the ground. Kept one in for lifelink.
1x Stubborn Denial - Few important non-creature spells. Removal prioritized over counters.
1x Otherworldly Gaze - Not getting us a card to hand makes Gaze slightly worse.

> Creativity (Temur / Izzet):

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 can combo faster than creativity and then play the control game, but there's an element of luck to it, the matchup isn't terrible, but you need to be careful. Either resolve Soulflayer fast and close the game, or wait until they're low on resources and capitalise.
The plan game one is simply to resolve a Soulflayer, doesn't have to be particularly strong, hexproof / indestructible + 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:
3x Mystical Dispute - More disruption early, hits their counters and makes sure our threats resolve.
2x Duress - Taking their combo pieces or interaction, either slowing them down or poking a hole for us to combo through.

Out:
2x Vampire of the Dire Moon - Deathtouch and lifelink don't help against combo control.
2x Striped Riverwinder - There's less relevant removal in the matchup and most is damage based. Happy to cut a copy of hexproof.
1x Otherworldly Gaze - This matchup will be about interaction, so trimming something that doesn't actually put cards in hand is the call here.

>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.
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 9 sideboard cards in. Same as game one, prioritize lifelink and hexproof to make an impossible to remove Soulflayer as soon as possible.

Changes:

In:
3x Ray of Enfeeblement - Hits every creature in the deck
2x Path of Peril - A way for us to stabilise if they're going too fast.
2x Abrupt Decay - Hits every creature and Rest in Peace.

Out:
3x Thoughtseize - Hand interaction is less important in the aggro matchup.
2x Rona's Vortex - We have much more efficient removal spells for Humans.
1x Striped Riverwinder - They have little removal so shaved two hexproof sources.
1x Stubborn Denial - They have few noncreature spells, much less useful here.

>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 significantly more disruption.
Game one should be relatively straightforward, if difficult, block with Ledger Shredders, fight through disruption, resolve a Soulflayer when you can, win from there.

Post-Board:

Mostly the same, apart from the vague threat of turn two Rest in Peace, if this happens we can block with Shredders and try to gain life back with Vampires and Banehound. It's harder, but not impossible. Most lists seem to have steered away from RiP, so hopefully your Spirits opponent has too.

Changes:

In:
3x Mystical Dispute - Will hit most, if not all of their spells.
2x Path of Peril - A way for us to stabilise if they're going too fast.
2x Abrupt Decay, - Most lists seem to have stopped playing Rest in Peace, but this deals with that, as well as all of their creatures, through counterspells.

Out:
2x Otherworldly Gaze - Needing to interact early means Gaze is slightly less good, especially when we want to keep cards in hand.
2x Striped Riverwinder - They run limited removal. We should aim to have counterspells up or have already discarded their tempo plays, so going down on other angles of protection is fine.
2x Rona's Vortex - We have better removal to bring in for Spirits.
1x Stubborn Denial - Even though they have lots of disruption, they're a tempo deck, creatures are their main plan, Mystical Disputes are our counter of choice.

>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 running into a Soulflayer with vigilance.

Changes:

In:
2x Path of Peril - A way for us to stabilise if they're going too fast.
2x Abrupt Decay - While not ideal, forcing them to find another creature is relevant tempo against a very fast deck.
1x Glissa Sunslayer - Very hard to attack into.

Out:
4x Thoughtseize - The life loss hurts. Good disruption, but not where we want to be.
1x Striped Riverwinder - Very little that can kill a Soulflayer, trimmed two.

*Less Tested Matchups

> Gruul Midrange:

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.

Changes:

In:
2x Abrupt Decay - Destroys every creature in the deck.
1x Glissa Sunslayer - Very hard to attack into.

Out:
2x Striped Riverwinder - The biggest targeting threat to worry about is The Akroan War, but we can hopefully use our removal and disruption to make sure it never sticks around for long.
1x Stubborn Denial - They're mostly creature based, while they have some enticing targets, it's not worth it to have a mostly dead card for the small chance of a blowout.

> 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 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.
Rest In Peace - Shuts down the graveyard.

Changes:

In:
3x Ray of Enfeeblement - Removes any creature for one mana, great way to stop their early developments.
2x Abrupt Decay - Removes every non-land permanent in their deck, including RiP
1x Assassin's Trophy - Used mostly as a second copy of Abrupt Decay

Out:
2x Striped Riverwinder - Very little removal that hits Soulflayer, Scavengers is a bit more vulnerable, but cutting some Hexproof doesn't feel too bad.
2x Rona's Vortex - Bouncing a creature isn't too useful as they'll replay it again and trigger all their other permanents.
1x Vampire of the Dire Moon - No blocking will be done as all their threats fly, keeping in one for the lifelink.
1x Stubborn Denial - They have a few good targets, but mostly dead.

>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.

Changes:

In:
3x Mystical Dispute - Will hit all of their counters
2x Abrupt Decay - Hitting Thing in the Ice is key as it's one of their only ways of stopping a Soulflayer
1x Assassin's Trophy - Essentially a second copy of Abrupt Decay.

Out:
2x Otherworldly Gaze - Needing to interact early means Gaze is slightly less good, trimmed two.
2x Vampire of the Dire Moon - No blocking will be done as all of their threats fly.
1x Striped Riverwinder - They run limited removal. We should aim to have counterspells up or have already discarded their tempo plays, so going down on other angles of protection is fine.
1x Stubborn Denial - Bringing in three Mystical Dispute means we can cut the worse counterspell.

>Five-Colour Midrange:

Their Problem Cards:

Fires of Invention - One of the possible engines of the deck.
Bring to Light - One of the possible engines of the deck.
Rest in Peace - Shuts down our entire gameplan.
Various targeted exile effects - Need Hexproof.

Changes:

In:
2x Abrupt Decay - Removes their early enchantments, notably RiP.
1x Assassin's Trophy - Kills the bigger threats if they have time to stabilise.
1x Glissa Sunslayer - Removes their bigger enchantment and threats.

Out:
2x Vampire of the Dire Moon - Chip damage isn't relevant.
2x Consider - Not needing to go quite as fast means consider can come out for more impactful cards.

>Boros Convoke:

Their Problem Cards:

Gleeful Demolition - Essentially Dark Ritual in this deck, insane acellarant.
Venerated Loxodon - Gives a buff to their creatures and adds a medium sized body.
Reckless Bushwhacker - Turns a small push into a lethal attack.
Knight-Errant of Eos - Draws them cards and allows them to keep up pressure.

Changes:

In:
3x Ray of Enfeeblement - Removes their one drops or bigger threats.
2x Path of Peril - Will hit all of their tokens.

Out:
2x Striped Riverwinder - Next to no removal in their deck. A Giant Killer is all that we need to worry about.
2x Otherworldly Gaze - The first few turns will need interaction, so we can go down a few one drop dig spells.
1x Consider - Interacting early is key so other one drops come out.

>Boros Pia Aggro:

Their Problem Cards:

Chained to the Rocks - Not awful as we have enchantment removal and hexproof, but something to watch out for.
Pia Nalaar, Consul of Revival - Goes very wide if left unchecked.

Changes:

In:
2x Path of Peril - Will hit all their creatures if they're getting too far ahead.
2x Abrupt Decay - Some decks run Rest In Peace, this hits that while also removing creatures if needed. Also hits Invasion of Gobakahn from the board.

Out:
2x Thoughtseize - Hitting a creature from their opener is nice, but is a terrible topdeck late game.
1x Striped Riverwinder - Limited removal means we can trim the some hexproof effects.
1x Stubborn Denial - A lot of their cards aren't worth countering as they have such high card velocity.

>Lotus Control

Their Problem Cards:

Strict Proctor - Slows down Urborg Scavengers, allows them to play Lotus Field with no downside.
Discontinuity - We need to be careful doing things on their end step as they can just exile our spell for two mana, as with regular control, we have to wait until we have counterspell backup or they tap out before trying anything important.
Sunfall / Farewell - Three exile-based wraths mainboard is difficult, watch out for these and be ready to fight them.
Rest in Peace - Shuts down our gameplan hard.

Changes:

In:
3x Mystical Dispute - Interacting early is key here, hitting RiP or resolving something through an Absorb is great.
2x Duress - For shredding their hand, keeping them low on resources and trying to pick a hole in their defences.
1x Glissa Sunslayer - An additional threat that can kill Planeswalkers, draw cards and remove graveyard hate.

Out:
2x Vampire of the Dire Moon - Lifelink doesn't help here and they're not going to beat down on their own.
2x Otherworldly Gaze - Gaze not drawing a card in the grinder matchups is a fairly big issue
1x Banehound - Keywords aren't relevant and a 1/1 isn't enough of a threat.
1x Consider - Trimming one for more impactful cards.

>Archfiend Combo

Their Problem Cards:

Archfiend of the Dross / Metamorphic Alteration - these, together, can make us lose the game on our upkeep.
Extinction Event - Can remove a Soulflayer no matter what we do. Hold your counters for these if you can.

Changes:

In:
3x Mystical Dispute - Creature-light matchup, countering wraths and draw spells will be important.
2x Duress - Discards their Fable of the Mirror Breakers, Metamorhpic Alteration etc.
1x Assassin's Trophy - Can remove any permanent if and when we need it.

Out:
2x Vampire of the Dire Moon - Lifelink doesn't help here and they're not going to beat down on their own.
2x Otherworldly Gaze - The earlier turns will be spent interacting, so going down some Gazes here feels safe.
1x Striped Riverwinder - Outside of Alteration, very little actually can remove our creatures, trimmed one.
1x Stubborn Denial - Mystical Dispute will get the job done better here.