Consider:
* Dauthi Voidwalker - Graveyard hate and a possible way to get a wincon
* Sinister Concoction - Enchantment-based cheap removal that also mills me
* Nihil Spellbomb - Cheap graveyard hate that can also be used to cycle and just use my artifact drop for turn
* Eternal Witness - Get back important stuff when I can't have Muldrotha, or just Villainous Wealth
* Stitcher's Supplier

More basics
Temple of Mystery
Exotic Orchard
Flooded Strand

Demon's Disciple - A Fleshbag that can also hit superfriends decks
Seal of Doom - Cheap removal, but can't hit black creatures
Vile Entomber - A deathtouchy Entomb on a stick
Skull Prophet - Dork that can also self-mill
Rootcoil Creeper - Dork that makes any color, and two mana if used with Muldrotha
Mazirek - Make my dorky dudes actually able to win
Viscera Seer
Risen Reef - I actually have some Elementals to trigger this multiple times. Sick with Mulldrifter evoke
* Foundation Breaker - Evoke enchantment/artifact removal
Cemetery Tampering - Basically card draw
Deathrite Shaman - Graveyard hate with a splash of ramp, lifegain or burn
Coiling Oracle
Liquimetal Torque - Allow Caterpillar and friends to destroy anything
Khalni Heart Expedition
Kenrith's Transformation
Oko, Thief of Crowns
Squandered Resources
Tormod's Crypt - Cheap, one-sided graveyard hate
Oriq Loremage - Repeatable Entomb on a stick
Jarad - Some reach on a big body
* Uro - An actual threat, great value and a way to use my yard if I can't have Muldrotha, but more needed in Niv
Expedition Map
Guardian Project
Engineered Explosives - Probably busy in modern/legacy
Thassa's Oracle
Sylvan Safekeeper - Protect Muldrotha
Noxious Gearhulk - Two card types and removal
Tomebound Lich
Talisman of Curiosity - What other deck is going to use these?
Control Magic
Narset, Parter of Veils
Font of Fertility - A reusable Rampant Growth
Skullclamp
Omen of the Sea
Imprisoned in the Moon
Grist
Titania - Get some threats from repeatable fetches
Riftsweeper - Shuffle back combo pieces after exile
Mystic Snake - Counterspell
Bazaar Trademage
Atris, Oracle of Half-Truths
Neurok Stealthsuit - Protection for Muldrotha
Nimble Obstructionist - Can stifle a Bojuka Bog or similar, then is a cheap flying beater
Bane of Progress
* Ashnod's Altar/Phyrexian Altar
World Shaper - Probably needs sac outlets
Vraska, Swarm Eminence
Lockets
Bone Shredder
Oblivion Stone
Hythonia the Cruel - Sweeper
Wave of Terror
Sanguine Praetor - Sac outlet and partial sweeper
Plague Boiler
Phyrexian Scriptures
Tetzimoc - Sweeper
Yavimaya Elder
Path of Discovery - Basically card draw
Woodfall Primus
Laboratory Maniac
Search for Azcanta
Llanowar Elves/Elvish Mystic
Nyx Weaver
High Market

Consider (don't have):
* Tormod, the Desecrator - Get a zombie for every card I cast from the yard
$ Cephalid Coliseum - Triple loot in the land slot
$ Elephant Grass - Ghostly Prison that can completely stop black creatures, and I can just let it die and recast it upkeep is too much. However I probably have enough dorky dudes to chump most attacks
Mindslaver
Unbridled Growth - Use my enchantment slot and  mana to draw a card, or even fix early
$ Vraska, Golgari Queen
Old Rutstein
Vilespawn Spider - Self-mill and token generation
Port of Karfell
$$$ Yarok, the Descrated
$ Phenax - Wincon?

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Consider (non-permanents):
* Fact or Fiction
* Buried Alive
* Counterspell
Living Death
Life From the Loam
Primal Surge - Would probably also want Lab Man as backup in case Jace is already gone
Jarad's Orders
Archaeomancer - Permanent, but doesn't make sense without any other non-permanents
Cyclonic Rift
Grisly Salvage

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Considered cuts:
Meren - I'm not really a reanimator deck, so I don't have a lot of huge stuff to cheat out, and I can already get stuff out of the yard with Muldrotha. Also don't have a huge amount of sac outlets to gain experience fast
Night Incarnate - Sweeper, but only for small/medium sized creatures, which includes most of my stuff
Izoni - The sac is expensive, and if I don't get at least 4-5 tokens it's probably not worth the cost
Birthing Pod - Need to have multiples at every part of the chain for this to work
Executioner's Capsule - Depending on the meta, finding targets might be difficult
* Sultai Ascendancy - A bit slow
Acidic Slime - 5 mana might be a bit much for this effect
Villainous Wealth - The only non-permanent

* Golgari Rot Farm - ETBT, but helps a bit with a low land count
Terramorphic Expanse/Evolving Wilds - Some fetches are nice, but these will always fetch tapped so maybe the other fetches are enough?
* Tranquil Thicket - Cycle first then play from the yard is nice, but then it enters tapped and I can't do it again
Breeding Pool - Kalamax needs one, will take from here or Roon

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Cuts:
Elixir of Immortality - I don't really want to use this
Viridian Zealot - Too heavy green
The Mending of Dominaria - Slow and expensive self-mill with relatively minor effect
Deadbridge Chant - Expensive and time-consuming
Golgari Thug
Deathreap Ritual
Garruk Wildspeaker - Put in a mono-green deck?
Garruk, Apex Predator - Very high CMC, and not immediately game-winning
Kiora, Master of Depths - I'm never going to get to the ult, and the other abilities are a little meh
GGT/Stinkweed Imp/Dakmor Salvage - Unlike Loam, they don't have a way to get back to the yard. The Imp is at least cheap to cast and can then be sacced, but other ways to mill might be preferred
Dreamborn Muse - Helps fuel my yard, but also does the same for my opponents which I might want to avoid since I'm not winning by mill. Also doesn't do anything until the next turn
Frilled Mystic - Expensive for a counterspell, and with a very specific cost. The thing most likely to get countered is Muldrotha, which means I need this in hand and an extra 4 mana, which is a big ask. When Muldrotha is resolved, there might be better "counters"
? Attrition - Need things to sac, and can't kill everything
Vannifar - Is this worth it without a combo? Without haste she will probably die before she can be used, and even then the value is moderate
Taigam - Only affects my draw step, and while the spot removal is nice, I don't really want to exile my yard. Probably not worth 5 mana
? Talisman of Resilience - Might have enough with the other rocks, and this one hurts
Artifact lands - I don't have extra land drops or any particular synergies with these, so there's no reason to expose myself to an additional axis of hate
Bouncelands - ETBT, but helps a bit with a low land count. 3 might be too much
? Dakmor Salvage - Unlike Loam, it doesn't have a way to get back to the yard, but it could potentially get pretty deep with Gitrog
Emergence Zone - I can't play things with Muldrotha on other people's turns, so the flash isn't super relevant except to secure more mana for the first turn with her, or flash in something like a Baleful Strix, so being colorless is probably not worth it Cycling lands - Cycle first then play from the yard is nice, but then they will enter tapped and I can't do it again
Burnished Hart - Having two card types is nice, but casting and using this is quite costly, and I'm likely to run out of basics. Farhaven Elf is probably just a better replacement
Champion of Wits - Doesn't actually net any cards until embalmed, but it does fuel the yard at the cost of no cards
Mesmeric Orb - Might not want to help my opponents fill their yard, and I don't need to turbo fill mine if I can just draw cards instead
Garruk, Cursed Huntsman - Quite expensive
Tamiyo, Collector of Tales - Too vulnerable, will probably die after one activation, making it a 4 mana Regrowth or 4 mana mill 4
Phyrexian Tower - More needed in Braids