Essentially the synergy is to have Lurrus (100% guaranteed) and Kaya's Ghostform (you'll draw it eventually) and use it for all the sacrifice synergies you need. For example, if you have Lurrus and the Ghostform, all it costs is {1}{B} to drain an opponent for 1 with Pitiless Pontiff and Cruel Celebrant out. Bonus points if you have one or more Hateful Eidolon out, as that loop additionally nets you a card.
Wowee, something combos with Phyrexian Altar. As the original deck was standard, I didn't have that luxury. You can add it if you want.
Overall, it sucks to not be able to play Ayara, First of Locthwain. It might be better to just run Lurrus in the main 60 so you can add her and other GY deck bombs like either Ereboses or even the new Luminous Broodmoth. Overall I think just having a super consistent combo to rely on really shows how broken Companion is.
I've been playing things like this myself. Lurrus is a ton of fun to build around . This set has so many amazing cards for these sacrifice-based decks including Serrated Scorpion, Whisper Squad and Fiend Artisan. I also plan to build something like:
The easiest, and probably most competitive way to use Lurrus is in shells that alreday played few to no 3+ CMC cards, where it's pure value as a free-roll. One-drop aggro with all the Pulse Tracker variants, Soul Sisters, and "Cheerios" style decks with Puresteel Paladin and Sram, Senior Edificer +0-1 CMC equipment come to mind.
These cards have the advantage of working synergistically with Lurrus with no other pieces required, and if you can fit a few of them into a cohesive decklist, the value should flow.
I've been doing lots of card research to write this up, and hopefully I cover the best ways to break Lurrus of the Dream-Den, but ultimately I'm expecting you all to break him with your own awesome decklists...
So, upon release it was quickly obvious how powerful Lurrus is, but as a non-companion in a control/toolbox theme, I think this can be exploited even further in modern, and there are already some pretty powerful Lurrus decks out there. It really opens the door for various themes to thrive, and even allows for some downright absurd combo value to exist (hint: Enigmatic Incarnation and Hatching Plans).
Lurrus opens an interesting door for self-sacrificing counterspell creatures like Voidmage Prodigy, Siren Stormtamer, Cursecatcher, Mausoleum Wanderer, Spiketail Hatchling, and Judge's Familiar, which all benefit from being effects, versus spells that can be countered easier. Voidmage is an awesome engine for turning wizards into hard counters (then Lurrus completes the cycle of replenishment), making S.Stormtamer and Cursecatcher top considerations as small wizard-counterspells that can help control and/or slow the early game before Voidmage gets out. M.Wanderer, S.Hatchling and J.Familiar are non-wizard alternatives worth consideration, pending your desired theme. If you stick with wizards a little for Voidmage you can find viability in 1cc wizards like Grim Lavamancer, Viscera Seer, Sage of Epityr, Overwhelmed Apprentice, Soul-Scar Mage, God-Pharaoh's Faithful, Benthic Biomancer, Cosi's Trickster, (etc,) and for 2cc there's Dark Confidant, Augur of Skulls, Qasali Pridemage, Baral, Chief of Compliance, Dreadhorde Arcanist, Senate Guildmage/Dismissive Pyromancer, Asylum Visitor/Blood Scrivener, Drannith Magistrate, Azorious Guildmage, Meddling Mage, and many others, but these seem to be worth the most consideration with Lurrus. Additionally, Guile becomes a very intriguing option under Voidmage's umbrella, since you're not likely to win early, and getting it on the BF changes the impact of your counters dramatically. So the simple goal will be to have enough cheap and usable control spells and sac-creatures in your opening hand to stall your opponent's efforts until you can get four or five lands that tap for blue, Voidmage, a cheap wizard (or two, but Voidmage can sac itself), and Lurrus... then you should be pretty well in control of the game. Remember, your counterspells from Voidmage can't easily be countered, so their impact with each recurred use is quite game changing, and basically requires Stifle to battle it. So sideboard Stifle against other Voidmage/Lurrus decks...
For extra "redundancy" in your Lurrus engine for creatures, throw in Athreos, God of Passage too... once both are out, every creature you sacrifice comes right back to your hand, unless your opponent takes 3 damage and lets you recur it with Lurrus. That means if you continuously sac and re-cast something, they need to take 6 damage to force it into your grave... so that Lurrus can get it back on your next turn. Ouch.
Before we go further I'd like to run through my favorite cards that have good synergy with Lurrus (in no particular order, or care about color):
The trio of Lurrus of the Dream-Den, Enigmatic Incarnation, and Hatching Plans, all under a "sacrificing" toolbox/control theme seems too good to pass up. Once running, every turn you essentially pay 2cc to draw three extra cards and search for a 3cc-or-less creature (Lurrus, then Uro...?) to put on the battlefield. Add in a range of sacrifice/recur/security pieces to protect the engine and you might be able to build an impenetrable force that resupplies itself with ease, once enough pieces are in play. Just get Lurrus and/or Athreos onto the BF and decently protected, and the game should be over pretty soon. For a little redundancy, you can use Ordeal of Thassa as a backup option to Hatching Plans, netting two cards instead of three.
Using the Enigmatic Incarnation/Lurrus engine opens the door for some other enchantments to consider sacrificing instead of Hatching Plans, like Ordeal of Heliod (sac with E.Incarnations to grab Voracious Wurm, and boom you gain 10 life and get a 12/12), Ordeal of Nylea, Oath of Ajani, Fists of Ironwood, Strength from the Fallen, or Rise of the Hobgoblins, to get Lurrus or other needed creatures onto the BF. But you can also use Cindervines for its obvious purposes, then double it as a sac option for E.Incarnation to search for a creature. Cindervines gives you the enchantment-sac flexibility for E.Incarnation, where Qasali gives you another wizard for Voidmage... your choice.
If you get to the point that you have Lurrus and Enigmatic Incarnation on the board with an appropriate enchantment to sac (and if the game isn't already over), you can search for a new creature each turn, and this makes a range of 2cc creatures viable in a deck as singletons that can be grabbed if needed (and reused with Lurrus if needed), like Grand Abolisher, Spellskite (although decking more than one also makes sense), Selfless Spirit, Timestream Navigator, Scavenging Ooze, Budoka Gardener, Kroxa, Titan of Death's Hunger (maybe x2 or x3?), etc. Since you are likely saccing a 2cc enchantment, other 3cc creatures fit this singleton niche for E.Incarnation to grab (they just aren't recursion targets for Lurrus), which likewise gives your sideboard lots of flexibility (and with Eladamri's Call, grabbing creatures from your deck should be relatively easy) and requires less 2x/3x/4x of a sideboard creature card.
While you can go various directions with a Lurrus based deck in modern, I keep coming back to the necessity of Voidmage and other wizards to establish initial control of the board. With three lands, Lurrus, Voidmage, and a 1cc wizard, you can hard counter a spell each turn and return your wizard to the BF with Lurrus, which all in itself becomes really hard for your opponent to handle since you're drawing cards and getting card advantage on top of it. Add a fourth land and another 1cc wizard, and it should be game over, assuming you can tap each land for blue (Realmwright?). (This hints at the desirability for land that can tap for any color mana, which really isn't hard to swing these days... Mana Confluence, City of Brass, Gemstone Mine, Forbidden Orchard, and Reflecting Pool can populate 20 lands in your deck, so it's pretty easy to swing five colors in modern.) Eladamri's Call can help to get what you need quicker, and being an instant, you can cast it at the end of your opponent's turn, which helps a lot with Voidmage in action. Then it's time for Enigmatic Incarnation to go to work, hopefully with Hatching Plans, at which point you can flood your board really fast and effectively. BUT, using Enigmatic Incarnation is also kinda more "fun" than necessary, as the game should be in control and effectively almost over before E.Incarnation gets going, so is it worth putting in the deck, or using other cards for the kill...? Debatable. But it could be worse than having E.Incarnation on the board T4 with a 2cc enchantment to sac (and no Lurrus in hand or on the board), allowing you to grab Voidmage, Lurrus or Athreos. And for this reason I think we kind of have two decks going... one that is heavy on wizards for Voidmage and counter control, but no E.Incarnation, then a second deck for E.Incarnation and less focus on control through wizards (but still using some), and more use of enchantments. If there was an 80 card format for modern, then this would be great to combine into one massive assortment of recursion engines. Alas.
Keeping with Subira, if you plan to use enough planeswalkers or counters on permanents, then the proliferating creatures of Thrummingbird, Grateful Apparition, or Guildpact Informant are worth noting, as well as Throne of Geth. And while your choice of planeswalker(s) is dependant on your chosen theme, it's worth mentioning Vraska, Golgari Queen because of how well she fits the overall sac theme, and securing attack damage with Subira for the ultimate (the -3 speaks for itself)
Another obvious direction is utilizing other/more sac-engine cards. It's hard to find a two-card sac engine that is more effective than Enigmatic Incarnation and Hatching Plans (in concert with Lurrus, of course). That's not to say you can't find something just as effective, but... good luck? That being said, it's hard to argue against self-sacrificing cards that require no other cards to be effective and can be used ASAP, but you can get more out of a good sac engine, hopefully getting two effects for one sacrifice (or one really good effect, like with Voidmage).
The list runs a core like this:
Essentially the synergy is to have Lurrus (100% guaranteed) and Kaya's Ghostform (you'll draw it eventually) and use it for all the sacrifice synergies you need. For example, if you have Lurrus and the Ghostform, all it costs is {1}{B} to drain an opponent for 1 with Pitiless Pontiff and Cruel Celebrant out. Bonus points if you have one or more Hateful Eidolon out, as that loop additionally nets you a card.
Wowee, something combos with Phyrexian Altar. As the original deck was standard, I didn't have that luxury. You can add it if you want.
Of course, you can only add permanents with CMC 2 or less. For multiplayer, I might be inclined to add Zulaport Cutthroat. In addition, I'd run Ayli, Eternal Pilgrim or Cartel Aristocrat to replace Pitiless Pontiff. In addition, Gonti's Machinations comes back with Lurrus...
Overall, it sucks to not be able to play Ayara, First of Locthwain. It might be better to just run Lurrus in the main 60 so you can add her and other GY deck bombs like either Ereboses or even the new Luminous Broodmoth. Overall I think just having a super consistent combo to rely on really shows how broken Companion is.
1x Lurrus of the Dream-Den
Lands (24)
20x Swamp
4x Castle Locthwain
Creatures (26)
4x Cauldron Familiar
4x Serrated Scorpion
4x Whisper Squad
4x Zulaport Cutthroat
4x Priest of Forgotten Gods
4x Fiend Artisan
1x Tymaret, Chosen from Death
1x Lampad of Death's Vigil
4x Witch's Oven
2x Throne of the God-Pharaoh
4x Gruesome Menagerie
I've been playing things like this myself. Lurrus is a ton of fun to build around
1x Lurrus of the Dream-Den
Lands (24)
24x Land
Creatures (23)
4x Soul Warden
4x Soul's Attendant
4x Serra Ascendant
4x Ajani's Pridemate
4x Karlov of the Ghost Council
2x Vizkopa Guildmage
1x Ayli, Eternal Pilgrim
4x Authority of the Consuls
4x Swords to Plowshares
2x Dawn of Hope
2x Return to the Ranks
1x Dreadhorde Invasion
Guilds of Ravnica - Commander 2018 - Core 2019 - Battlebond - Dominaria - Rivals of Ixalan - Ixalan - Commander 2017 - Hour of Devastation - Amonket - Aether Revolt - Commander 2016 - Kaladesh - Conspiracy 2 - Eldritch Moon - Shadows Over Innistrad - Oath of the Gatewatch - Commander 2015 - Battle for Zendikar - Magic Origins - Dragons of Tarkir
Green - Blue - Red - White - Gold
Slightly less potent, but a lot more original would be decks which actually build around Lurrus and its ability. The natural way to abuse it would be to repeatedly sacrifice the highest-value permanents you can find for 2CMC or less. Some options which can sacrifice themselves include Arcbound Ravager, Children of Korlis, Black Lotus, Sakura-Tribe Elder, Coretapper, Engineered Explosives, Gonti's Machinations, Hope of Ghirapur, Kami of False Hope, Lion's Eye Diamond, Martyr of Frost, Martyr of Sands, Mishra's Bauble, No Rest for the Wicked, Quest for the Gravelord, Seal of Cleansing, Seal of Primordium, Seal of Fire, Selfless Spirit, Spore Frog, Urza's Bauble, Vampire Hexmage, and Wayfarer's Bauble.
These cards have the advantage of working synergistically with Lurrus with no other pieces required, and if you can fit a few of them into a cohesive decklist, the value should flow.
The other major way to build around Lurrus specifically is to make a deck with sacrifice outlets and fodder, and build around that theme more completely. Some permanents that get great value out of being repeatedly sacrificed and replayed include Blisterpod, Brindle Shoat, Cauldron Familiar, Tukatongue Thallid, Doomed Traveler, Feral Prowler, Festering Mummy, Grim Initiate, Hunted Witness, Mogg War Marshal, Primal Druid, Veteran Explorer, Viridian Emissary, Baleful Strix, Burglar Rat, Dockside Extortionist, Ichor Wellspring, Oath of Nissa, Sarcomancy, Satyr Wayfinder, Servo Schematic, Stitcher's Supplier, Stoneforge Mystic, and Yarok's Fenlurker.
You'll want to combine the sacrifice fodder with sacrifice outlets such as Altar of Dementia, Carrion Feeder, Goblin Bombardment, Viscera Seer, Witch's Oven, Skullclamp, and Priest of Forgotten Gods. Add some sources of value from death triggers like Blood Artist, Cruel Celebrant, Zulaport Cutthroat, and Impact Tremors and you have a deck!
While Lurrus makes it tempting to load up on permanents, mass reanimation such as Return to the Ranks, Immortal Servitude, Wake the Dead, and Rally the Ancestors can be outstanding, as can spell-based token makers like Sylvan Offering.
So, upon release it was quickly obvious how powerful Lurrus is, but as a non-companion in a control/toolbox theme, I think this can be exploited even further in modern, and there are already some pretty powerful Lurrus decks out there. It really opens the door for various themes to thrive, and even allows for some downright absurd combo value to exist (hint: Enigmatic Incarnation and Hatching Plans).
Lurrus opens an interesting door for self-sacrificing counterspell creatures like Voidmage Prodigy, Siren Stormtamer, Cursecatcher, Mausoleum Wanderer, Spiketail Hatchling, and Judge's Familiar, which all benefit from being effects, versus spells that can be countered easier. Voidmage is an awesome engine for turning wizards into hard counters (then Lurrus completes the cycle of replenishment), making S.Stormtamer and Cursecatcher top considerations as small wizard-counterspells that can help control and/or slow the early game before Voidmage gets out. M.Wanderer, S.Hatchling and J.Familiar are non-wizard alternatives worth consideration, pending your desired theme. If you stick with wizards a little for Voidmage you can find viability in 1cc wizards like Grim Lavamancer, Viscera Seer, Sage of Epityr, Overwhelmed Apprentice, Soul-Scar Mage, God-Pharaoh's Faithful, Benthic Biomancer, Cosi's Trickster, (etc,) and for 2cc there's Dark Confidant, Augur of Skulls, Qasali Pridemage, Baral, Chief of Compliance, Dreadhorde Arcanist, Senate Guildmage/Dismissive Pyromancer, Asylum Visitor/Blood Scrivener, Drannith Magistrate, Azorious Guildmage, Meddling Mage, and many others, but these seem to be worth the most consideration with Lurrus. Additionally, Guile becomes a very intriguing option under Voidmage's umbrella, since you're not likely to win early, and getting it on the BF changes the impact of your counters dramatically. So the simple goal will be to have enough cheap and usable control spells and sac-creatures in your opening hand to stall your opponent's efforts until you can get four or five lands that tap for blue, Voidmage, a cheap wizard (or two, but Voidmage can sac itself), and Lurrus... then you should be pretty well in control of the game. Remember, your counterspells from Voidmage can't easily be countered, so their impact with each recurred use is quite game changing, and basically requires Stifle to battle it. So sideboard Stifle against other Voidmage/Lurrus decks...
For extra "redundancy" in your Lurrus engine for creatures, throw in Athreos, God of Passage too... once both are out, every creature you sacrifice comes right back to your hand, unless your opponent takes 3 damage and lets you recur it with Lurrus. That means if you continuously sac and re-cast something, they need to take 6 damage to force it into your grave... so that Lurrus can get it back on your next turn. Ouch.
Before we go further I'd like to run through my favorite cards that have good synergy with Lurrus (in no particular order, or care about color):
Underworld Breach gives access to everything (nonland) that Lurrus doesn't...
Return to the Ranks in a sac-heavy creature deck this is ideally cast soon after Lurrus ETB, to restock/reset your army/toolbox
Unearth insurance for Lurrus or any of your crucial small creatures
Call of the Death-Dweller tough competition with Unearth... both are good
Spellskite adds a nice layer of protection for Lurrus, which he can bring back with ease
Kaya's Ghostform same benefit as Spellskite, but likely only for Lurrus, but awesome protection! When K.Ghostform brings Lurrus back you immediately bring back K.Ghostform
Subira, Tulzidi Caravanner crazy good draw ability with a fleet of small creatures, plus all the unblockable damage
Tarmogoyf (of course...)
Hexdrinker
Death's Shadow
Speaker of the Heavens on T1, Heroes' Reunion T2, then tap to make a 4/4 angel...
Serra Ascendant keeping with the life-gain theme
Avatar of the Resolute if you run enough +1/+1 counter synergy
Grave Pact
Cindervines alternate to Qasali for artifact/enchantment removal, plus damage, but can serve a third purpose as fuel for Enigmatic Incarnation
Engineered Explosives (or Ratchet Bomb?) EE is better, especially on the first use, but Ratchet fits the Lurrus "multiple use" concept better
Baleful Strix EDH option... would be nice in modern too, but alas...
Gifted Aetherborn/Vampire of the Dire Moon
Sakura-Tribe Elder/Wayfarer's Bauble/Armillary Sphere/Expedition Map/etc
Implement of Malice and the other Implements (most are worthy, pending theme)
Pilfering Imp/Thrull Surgeon/Liliana's Steward if you don't like Augur of Skulls...?
Children of Korlis
Dragonmaster Outcast requires exiling with Lurrus on the BF
Kami of False Hope/Spore Frog
Mentor of the Meek
Hanweir Militia Captain this is value... assuming you are running a heavy enough creature theme
Rix Maadi Reveler once in the grave, Lurrus gives much better control over the timing of using Rix
Edge of the Divinity makes Lurrus into a 6/5 lifelinker for 1cc, etc
Dead Weight/Mire's Grasp/Sangrite Backlash/Death's Approach
Executioner's Capsule/Sinister Concoction/Underhanded Designs
Gatekeeper of Malakir
Untamed Kavu
Bogbrew Witch/Bubbling Cauldron/Festering Newt makes much more sense with Lurrus...
Weight of Conscience is viable creature removal if you run a tribal theme (like wizards...), and lets you get to their indestructible creatures
Skirsdag High Priest great way to use sac-creatures before you sac them, etc
Wreath of Geists (opposite of Death's Approach) sac a creature, this pumps... your sacced creatures now matter more...
Wildborn Preserver becomes a solid mid/late-game mana outlet when you are casting creatures every turn and possibly dropping land every turn
Sleeper Dart
Glaring Spotlight
Saving Grace use first on defense with flash, then later on offense before an all-out attack
Seal Away and other similar cards...
Mishra's Bauble is free, so it's good early, but in mid/late game Lurrus will have better/bigger options to bring back, so...
Evolutionary Leap have enough redundancy in wizards on the board? Trade them for other creatures into your hand... fast...
Mogg War Marshal not crazy powerful, but it's still two 1/1's every turn for 2cc...
Vampire Hexmage sideboard for PW heavy decks, etc
Bounty Agent (for their creature commander)
Soul Tithe repetitively tie up mana or force sacrifices
Vexing Devil
Charming Prince is a decent option to be sacrificed by something else
Prized Amalgam it's faster to action in dredge, but it'd be a crime not to mention it
Niambi, Esteemed Speaker prevent a Path/Push from removing a creature, then trade extra legendaries for a couple cards, in between attacks under Subira?
Grafted Wargear is great if you're running a creature sacrifice engine, and especially benefits Mausoleum Wanderer
Narnam Renegade
Thieves' Guild Enforcer/Jace's Phantasm/Vantress Gargoyle for mill decks...?
Kargan Dragonlord
Throne of Geth sac to itself
No Rest for the Wicked use every turn you sac/lose more than one creature, return with Lurrus; redundancy for Athreos; allows creature wipes to affect you less
Keldon Marauders a weak card (unless you can pump the damage), but has synergy... so, go wild
Grumgully, the Generous/Good-Fortune Unicorn low synergy with Subira's draw effect; helps Maus.Wanderer and Bitterblossom (etc); the more creatures ETB, the more this helps
*Hatching Plans with Enigmatic Incarnation (then Blood Aspirant, Slaughter-Priest of Mogis, or Auratog as "redundancy" options to sac enchantments)
The trio of Lurrus of the Dream-Den, Enigmatic Incarnation, and Hatching Plans, all under a "sacrificing" toolbox/control theme seems too good to pass up. Once running, every turn you essentially pay 2cc to draw three extra cards and search for a 3cc-or-less creature (Lurrus, then Uro...?) to put on the battlefield. Add in a range of sacrifice/recur/security pieces to protect the engine and you might be able to build an impenetrable force that resupplies itself with ease, once enough pieces are in play. Just get Lurrus and/or Athreos onto the BF and decently protected, and the game should be over pretty soon. For a little redundancy, you can use Ordeal of Thassa as a backup option to Hatching Plans, netting two cards instead of three.
Using the Enigmatic Incarnation/Lurrus engine opens the door for some other enchantments to consider sacrificing instead of Hatching Plans, like Ordeal of Heliod (sac with E.Incarnations to grab Voracious Wurm, and boom you gain 10 life and get a 12/12), Ordeal of Nylea, Oath of Ajani, Fists of Ironwood, Strength from the Fallen, or Rise of the Hobgoblins, to get Lurrus or other needed creatures onto the BF. But you can also use Cindervines for its obvious purposes, then double it as a sac option for E.Incarnation to search for a creature. Cindervines gives you the enchantment-sac flexibility for E.Incarnation, where Qasali gives you another wizard for Voidmage... your choice.
If you get to the point that you have Lurrus and Enigmatic Incarnation on the board with an appropriate enchantment to sac (and if the game isn't already over), you can search for a new creature each turn, and this makes a range of 2cc creatures viable in a deck as singletons that can be grabbed if needed (and reused with Lurrus if needed), like Grand Abolisher, Spellskite (although decking more than one also makes sense), Selfless Spirit, Timestream Navigator, Scavenging Ooze, Budoka Gardener, Kroxa, Titan of Death's Hunger (maybe x2 or x3?), etc. Since you are likely saccing a 2cc enchantment, other 3cc creatures fit this singleton niche for E.Incarnation to grab (they just aren't recursion targets for Lurrus), which likewise gives your sideboard lots of flexibility (and with Eladamri's Call, grabbing creatures from your deck should be relatively easy) and requires less 2x/3x/4x of a sideboard creature card.
While you can go various directions with a Lurrus based deck in modern, I keep coming back to the necessity of Voidmage and other wizards to establish initial control of the board. With three lands, Lurrus, Voidmage, and a 1cc wizard, you can hard counter a spell each turn and return your wizard to the BF with Lurrus, which all in itself becomes really hard for your opponent to handle since you're drawing cards and getting card advantage on top of it. Add a fourth land and another 1cc wizard, and it should be game over, assuming you can tap each land for blue (Realmwright?). (This hints at the desirability for land that can tap for any color mana, which really isn't hard to swing these days... Mana Confluence, City of Brass, Gemstone Mine, Forbidden Orchard, and Reflecting Pool can populate 20 lands in your deck, so it's pretty easy to swing five colors in modern.) Eladamri's Call can help to get what you need quicker, and being an instant, you can cast it at the end of your opponent's turn, which helps a lot with Voidmage in action. Then it's time for Enigmatic Incarnation to go to work, hopefully with Hatching Plans, at which point you can flood your board really fast and effectively. BUT, using Enigmatic Incarnation is also kinda more "fun" than necessary, as the game should be in control and effectively almost over before E.Incarnation gets going, so is it worth putting in the deck, or using other cards for the kill...? Debatable. But it could be worse than having E.Incarnation on the board T4 with a 2cc enchantment to sac (and no Lurrus in hand or on the board), allowing you to grab Voidmage, Lurrus or Athreos. And for this reason I think we kind of have two decks going... one that is heavy on wizards for Voidmage and counter control, but no E.Incarnation, then a second deck for E.Incarnation and less focus on control through wizards (but still using some), and more use of enchantments. If there was an 80 card format for modern, then this would be great to combine into one massive assortment of recursion engines. Alas.
Now Subira, Tulzidi Caravanner is hard to leave out in general, but in a RWB scheme, she becomes super valuable and might be a solid alternative plan to using Enigmatic Incarnation. She gives you big-time draw ability, for relatively cheap, and allows for unblocked damage every turn, which is awesome with a fleet of small wizards or creatures otherwise waiting to be sacced. (Honestly, Subira makes for an intriguing commander option.) This in itself opens the door to other 2-power and under creatures that wreak havoc with combat damage-triggered effects or untapping effects, like for 1cc/2cc there's Hope of Ghirapur, Copperhorn Scout, Honored Hierarch, Hapatra, Vizier of Poisons, Emmara, Soul of the Accord, Robber of the Rich, Grim Flayer, Skyknight Vanguard, Precinct Captain, Riptide Pilferer, Grateful Apparition, Tithe Drinker, Disciple of Deceit, Pain Seer, Wharf Infiltrator, or for 3cc there's Varragoth, Bloodsky Sire, Spawnwrithe, Dimir Cutpurse, Thada Adel, Acquisitor, Daring Thief, Thief of Sanity, Surrakar Spellblade, Augury Adept, Siren of the Silent Song, Cephalid Constable, Cold-Eyed Selkie, Daxos of Meletis, Graveblade Marauder, Ohran Viper, Prophetic Flamespeaker, Tandem Lookout, Sea-Dasher Octopus, Nightveil Specter, or Tomebound Lich, and Trygon Predator or Feline Sovereign for support. Above 3cc there are options like Akki Underminer, Glint-Eye Nephilim, Guul Draz Specter, King Macar, the Gold-Cursed, Seafloor Oracle, or Throat Slitter. There are also tons of good infect creature that can slide in under Subira's protection, potentially ending the game that much quicker.
Keeping with Subira, if you plan to use enough planeswalkers or counters on permanents, then the proliferating creatures of Thrummingbird, Grateful Apparition, or Guildpact Informant are worth noting, as well as Throne of Geth. And while your choice of planeswalker(s) is dependant on your chosen theme, it's worth mentioning Vraska, Golgari Queen because of how well she fits the overall sac theme, and securing attack damage with Subira for the ultimate (the -3 speaks for itself)
Another obvious direction is utilizing other/more sac-engine cards. It's hard to find a two-card sac engine that is more effective than Enigmatic Incarnation and Hatching Plans (in concert with Lurrus, of course). That's not to say you can't find something just as effective, but... good luck?