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.

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.
Adult Gold Dragon - With haste becoming more useful, the first copy might be better than the third Gifted Aetherborn.
Cragplate Baloth - With haste becoming more useful this felt better than Nightveil Predator.
Invasive Surgery - One mana hard counter against Lotus, Atraxa and Creativity.
Test of Talents - A more versatile hard counter, mostly for combo.
Savage Summoning - Improves matches against heavy control decks like Azorius and Dimir.
Ritual of Soot - A way to stem the bleeding against aggro decks.

Sideboard Theory: (Sideboard currently WIP as testing new cards!)

> R/B 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:

Fairly hard to lose, their only relevant interaction mainboard is Graveyard Trespasser and Bloodtithe Harvester. Both are only at sorcery speed, so can be played around fairly 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.
All four Thoughtseize usually comes out here, but in this matchup it actually buys us time to get to our combo. Acting almost as a counterspell, taking creatures or relevant disruption before they can stabilise is key.

Changes:

In:
2x Abrupt Decay - Hitting a resolved threat is still necessary.
1x Assassin's Trophy - Two mana to clear away any problem permanent.

Out:
2x Thoughtseize - Taking disruption is good, but is an awful topdeck in the longer games, shaved two.
1x Tainted Indulgence - Worst two mana dig option in this matchup, taking 4 from Sheoldred, The Apocalypse doesn't feel great, shaved one.

> 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:
2x Abrupt Decay - Removes creature devotion or Kiora, good for keeping them on their combat plan.
1x Assassin's Trophy - Kills bigger threats like Karn and Cavalier, can even hit Nykthos.
1x Aether Gust - Bouncing a Storm the Festival is good, as is any big green blocked when attacking.

Out:
2x Thoughtseize - While they can be a combo deck, they have the beatdown plan too, don't want too much discard here.
2x Striped Riverwinder - Hexproof is less important against a deck with low removal. Cycling is still nice though.
1x Tainted Indulgence - Worst two mana dig option in this matchup, need to fill the graveyard faster and dig harder than this allows.

> U/W 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 Abrupt Decay - Hits Rest in Peace and occasionally tokens, almost exclusively for RiP though, as it's very hard to fight through.
2x Savage Summoning - Making a Soulflayer uncounterable and flash speed is incredibly good.
1x Assassin's Trophy - Hits RiP and all their planeswalkers.

Out:
2x Grisly Salvage - While this digs a lot of cards, it's the only one that can mill key instants that we have no chance to return. When the game will be won or lost on hitting ways to force our combo through, milling huge amounts of cards is risky.
1xTainted Indulgence - Trimmed one of the dig cards to fit in sideboard protection.
1x Otherworldly Gaze - Trimmed one of the dig options to fit in sideboard protection.
1x Samut, Voice of Dissent - Trimmed one to make space. Making every card count and be castable is important here. No Hexproof or Indestructible also leads Samut to be less valuable.

> Dimir Rogues:

Their Problem Cards:

Game One:

Post-Board:

Changes:

In:

Out:

> 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 Thoughtsieze - Unless I'm discarding an Akroan War or Skysovereign, this isn't worth it here.

> G/W 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.

> 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.

In:
3x Stubborn Denial - Usually win attempts will come after resolving a Soulflayer, meaning this is a hard counter for U.
2x Unmoored Ego - Essentially wins the game choosing Lotus Field, or if they already have one out, Thespian's Stage.
2x Thoughtseize - Hand disruption in the combo matchup is always good.

Out:
4x Fatal Push - Hits nothing meaningful in the deck
2x Gifted Aetherborn - Deathtouch and lifelink don't help in the combo race.
1x Tainted Indulgence - The worst of the card advantage spells.

>Mono-White Humans:

Their Problem Cards:
Brutal Cathar - Exiles a non-hexproof Soulflayer. Even if we get it back, it loses the keywords.
Brave the Elements - Allows them to get through damage, blank removal and force auras to fall off.
Rest in Peace - Shuts down our entire gameplan.
Thalia, Guardian of Thraben - as a low curve deck with few lands, adding 50%+ to the cost of our spells hurts.

In:
4x Abrupt Decay - Hits almost everything in the deck.

Out:
2x Thoughtseize - Hand interaction is much less important in the aggro matchup.
1x Adult Gold Dragon - No hexproof or indestructible.
1x Tainted Indulgence - The worst of the card advantage spells.

>Abzan Greasefang:

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

In:
4x Abrupt Decay - Kills Greasefang and Liliana unconditionally.
2x Unmoored Ego - Naming Greasefang means they have a hard time crewing vehicles, should slow them down enough for us to win.

Out:
4x Fatal Push - Doesn't kill Greasefang and all other creatures are only used for their etb effects.
2x Thoughtsieze - Nothing massively dislikes being in their graveyard.

>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.