LANDS
Barren Moor, Lonely Sandbar, & Tranquil Thicket- These are in the deck just for the Life from the Loam cheese, which is cycle, dredge 3, get Loam back, cast it, get the cycle land back, and repeat as much as you'd like.
Breeding Pool, Overgrown Tomb, & Watery Grave- The shock lands are a necessity for any deck that can run them, they are cheap price wise for how powerful they are, and being able to fetch them is important for any multicolored deck.
Cephalid Coliseum- One of the lands that are highly synergistic w/ Muldrotha, you can keep sacrificing this than play it again using Muldrotha, which feeds both the graveyard and our hand, plus Threshold is relatively easy to achieve in this deck.
City of Brass & Mana Confluence- Great lands that should be played in any multicolored deck, the 1 life cost is so miniscule in a format that starts you at 40 life.
Command Beacon- Sac this to get a Muldrotha w/ commander tax out of your command zone, then play this land out of your graveyard w/ Muldrotha, works similarly to Titania, Protector of Argoth
Command Tower- Best land for any multi-colored commander deck, an auto-include.
Exotic Orchard & Reflecting Pool- Usually just redundant Command Towers.
Ptismatic Vista- an auto-include in any multi-colored deck running a decent amount of basics, it's especially good in this deck, since it can be used over and over again, like the fetch lands, using Muldrotha.
7x Forest, 2x Island, & 6x Swamp- The deck wants to use a lot of basics, so you reuse your fetch lands over and over again & use Sakura-Tribe Elder over & over again.
Glacial Chasm- One of the most powerful cards in the deck, this will keep you alive while you assemble your combo, and this card's cumulative upkeep can be negated by just playing it again from the graveyard once you don't pay for it, resetting the age counters, even the ETB sac can be negated by just playing the land that you sacrificed from the graveyard using Muldrotha.
High Market- A sacrifice outlet on a land, allows you to sacrifice a creature which allows you to play it again using Muldrotha.
Misty Rainforest, Polluted Delta, & Verdant Catacombs- Fetch lands are arguably the best lands in magic, combos well w/ Muldrotha & Ramunap Excavator.
Morphic Pool, Undergorwth Stadium, & Rejuvenating Springs- Will almost always come into play untapped, a great new land coming out of Commander Masters (Battlebond).
Strip Mine & Wasteland- Recurable land destruction, just brutal.
Urborg, Tomb of Yawgmoth- Goes in every multicolored deck running .
INSTANTS
Entomb- Ends up being a 1 mana tutor if you have Muldrotha on the battlefield, just get whatever card you need.
Frantic Search- Feels like a "free" card since it costs you no mana, discards cards to your 2nd hand and draws you 2 cards, it's just amazing in this deck.
Memory's Journey- Protects you from losing the when going for the self mil win and you get disrupted.
Vampiric Tutor- Auto-include in any deck, one of the best cards in commander, second only to Demonic Tutor.
CREATURES
Birds of Paradise- One of the best cards in commander, turn one ramp is both incredibly rare and incredibly powerful.
Caustic Caterpillar- Self-sacrificing enchantment/artifact destruction attached to a creature, it being a creature makes it easy to tutor for in this deck, because of cards like Buried Alive and Jarad's Orders.
Deathrite Shaman- He's right up there w/ Birds of Paradise on the power level side, and it gives the deck some much needed graveyard hate, especially since this deck run Mesmeric Orb.
Dosan the Falling Leaf- The deck runs no instant speed removal, so this ends up being a one sided effect, benefiting you.
Eternal Witness- This a graveyard based deck w/ ways to abuse ETB triggers (by sacrificing the ETB creature then playing it again using Muldrotha), so you better believe that this deck runs one of the most popular & powerful ETB cards in commander.
Fauna Shaman- Most of the combo pieces in this deck are creatures, so that's usually what you'll grab w/ her, and remember discarding in this deck really means, "put this card into your second hand."
Glen Elendra Archmage- One of the few ways to counter spells using a permanent, luckily it's a pretty solid way to counter non-creature spells, also this card + Mikaeus, the Unhallowed is pretty silly.
Gravebreaker Lamia- Is the perfect card for the deck, it can tutor up combo piece into the graveyard to be cast using Muldortha, and it makes the spells cheaper to cast which can be incredibly useful, and it being an enchantment/creature makes more flexible to cast using Muldrotha, since you can chose one or the other for your once per turn permanent type.
Mikaeus, the Unhallowed- In the deck for multiple combos (see combo section).
Mindslicer- The deck runs a ton of sacrifice outlets, so killing this thing shouldn't be too difficult, and once you do, you get to put all the cards in your first hand into your second hand and all of your opponents get to discard their hands into their graveyards.
Mirror-Mad Phantasm- Unfortunately there isn't too many efficient ways to mill yourself in this deck, but this little guy gets the job done beautifully, just use 2 mana to keep milling yourself an absurd amount until you are sufficiently satisfied.
Mulldrifter- Evoked card draw that has an ETB that can be abused.
Mystic Snake- Another one of the few counterspells attached to a permanent, you are only going to be able to use Muldrotha's ability on your turn, so you're probably only going to use this critter from the graveyard to protect your combos when attempting to go off.
Plaguecrafter- Gives the deck a self-sacrificing way to put pressure on the creature side of your opponents' board.
Protean Hulk- In the deck to grab Mikaeus, the Unhallowed & Walking Ballista, which is a combo win con if you have an infinite sac outlet like Ashnod's Altar or Altar of Dementia.
Ramunap Excavator- The deck's already built around recurring lands from the graveyard using Muldrotha, so this naga is just a redundant version of that effect.
River Kelpie- This card will help you draw cards like crazy, even without the combo potential, speaking of which, the combo w/ this is River Kelpie + Mikaeus, the Unhallowed + infinite sac outlet + Thassa's Oracle, basically you just keep bringing River Kelpie back an infinite amount of times allowing you to draw an infinite amount of cards, which nabs you the self deckout win.
Sakura-Tribe Elder- Self-sacrificing ramp, exactly the type of card this deck needs.
Sidisi, Undead Vizier- A self-sacrificing tutor on a creature, just perfect for this deck, especially for finding the combo pieces.
Spore Frog- This deck does about the same thing a Meren of Clan Nel Toth deck does w/ this creature, which is giving you one Fog effect for each round around the table.
Sylvan Safekeeper- Gives protection to your creatures, which is desperately needed, especially since the deck doesn't run Swiftfoot Boots & Lightning Greaves and has very few counterspells, this card also gives you a gimmick to nab an extra mana in your mana pool by sacrificing a tapped land then playing it from the graveyard untapped as your land for the turn.
Thassa's Oracle- used to win once we've milled ourselves (see combo section for more details).
Triskelion- Strictly in the deck for the mike and trike combo (Mikaeus, the Unhallowed + Triskelion).
Viscera Seer- An infinite sacrifice outlet attached to a creature, a utility that this deck is in desperate need of.
Walking Ballista- In the deck to be searched up w/ Protean Hulk for the Walking Ballista + Mikaeus, the Unhallowed + infinite sac outlet combo.
SORCERIES
Buried Alive- The most powerful tutor in the deck, you're usually going to throw your combo pieces in the graveyard to be played using Muldrotha, you can cheese your way around the 1 creature clause by reanimating one of the targets using Animate Dead or Necromancy, if you are going for the mike and trike win, you can have Mikaeus, the Unhallowed be your creature and Triskelion be your artifact.
Demonic Tutor- The best card in commander, goes in every deck.
Diabolic Intent- This deck wants to sacrifice creatures anyways, so it's well worth the price for a redundant Demonic Tutor.
Jarad's Orders- Put one creature into your hand and another into your second hand, the targets are probably going to be Mikaeus, the Unhallowed & Triskelion.
Life from the Loam- A great way to self mil and ensure land drops, you can dredge as many times as you'd like if you have a cycle land in your first or second hand (your graveyard).
Traverse the Ulvenwald- Delirium should be relatively easy to achieve in this deck, and the deck has a huge range of creatures and lands to pick from, and remember to use this in a pinch if you have to, sometimes a basic land can be the best card for your current situation.
ENCHANTMETS
Animate Dead & Necromancy- They're great in any graveyard based deck, however they're mostly in the deck to get around Muldrotha's 1 creature per your turn clause, allowing you to basically put two creatures from your graveyard into play.
Carpet of Flowers- Great ramp attached to a permanent for just one mana, if you've never played this card just because you're afraid of your opponent's not having Islands, then you are a fool, even if there is just one Island on the field, than you just got yourself a Birds of Paradise, seems good to me, oh and also there is always someone playing , or your meta is full of bad players who don't use .
Elephant Grass- A one mana Ghostly Prison/Propaganda + hate against black for some reason, the cumulative upkeep is negated using Muldrotha.
Exploration- A card that's great in most decks, however it's easily abuseable in this deck where you can play a land like Strip Mine from your hand, then activate it, then play it again from your graveyard, there are all sorts of cute gimmicks you can do, so have fun.
Manabond- helps to accelerate Muldrotha out as quickly as possible, then you can get the cards back that you discarded using Muldrotha.
Mystic Remora- This enchantment is already arguably the best card draw spell in commander, however it's even more stupid in this deck, where you can basically ignore the cumulative upkeep cost and just keep playing it from your graveyard for one mana.
Pernicious Deed- One of the few ways a permanent can wipe the board, luckily it sacs itself too.
Seal of Primordium- Like Caustic Caterpillar, this is another self-sacrificing artifact/enchantment attached to a permanent.
Sinister Concoction- Creature removal on a permanent that mills you, puts a card in your first hand into your second hand, and is self sacrificing.
Sylvan Library- An auto-include in any deck, it's also convenient that it's a permanent.
ARTIFACTS
Altar of Dementia- This card enables you to mil yourself and provides the infinite sacrifice outlet for some of the essential combos.
Ashnod's Altar- An infinite sacrifice outlet that can get you some mana too.
Basalt Monolith- In the deck for the Mesmeric Orb + Basalt Monolith combo to mil yourself and win w/ Thassa's Oracle.
Birthing Pod- Gives you a way to search up creatures and gives you a way to sacrifice creatures.
Expedition Map- A recurable way to search up the myriad of lands in the deck.
Jeweled Lotus- Muldrotha being 6 mana can be annoying to get to at times, and this card helps tremendously to get Muldrotha on the field, plus any 0 drop cards are amazing w/ Muldrotha, since you can play the card right after casting Muldrotha. Whenever Muldrotha dies, it can really set you back to the point of easily loosing you the game, since 8 mana is way too much, however this card can really help mitigate this annoying problem that occurs in a lot of games.
Lotus Petal- A free way to net an extra mana each turn.
Mesmeric Orb- One of the best cards for any self-mil deck, but it's especially good in this deck for the Mesmeric Orb + Basalt Monolith combo.
Nevinyrral's Disk- A board wipe attached to a permanent.
Sol Ring- It's commander.
Wayfarer's Bauble- A recurable way to ramp in this deck.
PLANESWALKERS
Ashoik, Dream Render- this deck can take advantage of all the modes on this planeswalker, exiling your opponents' graveyards every activation and keeping them from being able to tutor are both annoying abilities that your opponents have to deal w/, plus we can mil 4 cards into our second hand, which is incredibly helpful.
Oko, Thief of Crowns- was the scourge of standard & modern before quickly being banned, however he's still a power house in the eternal formats too, especially commander. Being able to elk commanders (symbol:loyalty-plus 1) is an incredibly powerful effect, and is one of the best ways to deal w/ a commander, it can potentially shutdown a deck that is highly reliant on their commander to work properly. His other 2 abilities aren't particularly exciting, but having a way to Elk a creature once on each of your turns is just too good of an ability to pass up on.