Adding secret deck tech Second Chance for one-card combo with commander giving infinite turns for only every turn.

Muldrotha Combos

Doom Whisperer and Second Chance --> Unlimited extra turns and a way to get below 5 life while finding what you need.

Time Sieve and Myr Battlesphere --> Unlimited extra turns for every turn.

Magus of the Will is budget Yawgmoth's Will on a body that can be reanimated by Muldrotha. It lets you play instants and sorceries in your graveyard. Usually these will be big reanimation spells. Very effective with Splendid Reclamation and Early Harvest. You need to reanimate all lands in the graveyard and untap most of them in this way, but once you do you have access to a lot of mana and the ability to play the rest of the good stuff in the graveyard such as Rise of the Dark Realms. This leads to the big finisher:

Reanimate all creatures and bring back Prime Speaker Zegana, Sewer Nemesis, and Laboratory Maniac --> Draw cards equal to the number of cards in your graveyard. If that number is bigger than your library, you win. Add Disciple of Bolas to double the card draw.

Fleet Swallower is good for getting your graveyard going, and can be used as an attack against opponents' decks as well. Between this and Traumatize, these are the ways to get started.

Sacrifice Lord of Extinction or Consuming Aberration to Jarad, Golgari Lich Lord.

Tormod, the Desecrator creates a 2/2 zombie every time you play a land or any spell from the graveyard.

Wonder and Bower Passage --> creatures you control can't be blocked except by creatures with Reach.

Insidious Dreams --> Discard a bunch of permanenent cards, which is essentially just saving them for later, and then stack your deck with combos.

Forgotten Creation with Golgari Grave-Troll --> Every upkeep, you discard your hand, and then draw that many cards. Then, in your draw step, mill 6 and get the grave-troll back. Repeat every turn for some massive self-mill. It gets even better with Underrealm Lich.

Every graveyard based deck with ETB trigger creatures needs sac outlets. Both Viscera Seer and Undercity Informer were chosen because they help dig for combo pieces.

Alchemist's Refuge and Awakening --> Take an extra turn during each opponent's turn (but you can't cast stuff from the grave).

Mindslaver --> a salty, one-card combo that basically says "Pay during your main phase to control your opponent's next turn... every turn, forever."

I've seen Mulldrifter in a lot of Muldrotha decks, but Bequeathal is by far the best card draw deck tech available in its class.

Glacial Chasm is a one-card combo that basically says "sacrifice a land every turn, but you can't be attacked anymore." If you choose not to pay the cumulative upkeep cost, you just get rid of it and then you can attack with your creatures. Play it again in the post-combat main phase to stop any incoming attacks. This card is great.

Memnite is a really great card in this build. When you run out of mana, you're still able to cast it, and it's a great, repeatable sac outlet or chump blocker that just keeps coming back. Counts as an artifact or a creature.

Similarly, Jace's Phantasm is a one-mana 5/5. It's insane how good this card is. You just need to mill your opponents a little bit with Undercity Informer, Fleet Swallower, or Dreamborn Muse

Kodama of the East Tree is great with Muldrotha, because you will want to be casting stuff from the graveyard and generally ignoring your hand. Well, every time you get something from the grave, you can also get something from your hand.

Corpse Connoisseur out, Gravebreaker Lamia in.

Golgari Grave-Troll out, Doom Whisperer in.

Splinterfright out, Reclamation Sage in.

Overeager Apprentice out, Skull Prophet in.

Foster out, Tormod, the Desecrator in.

Torgaar, Famine Incarnate out, Jarad, Golgari Lich Lord in.

Azusa, Lost but Seeking out, Laboratory Maniac in.

Grave-troll and splinterfright are great for different decks, but in this deck I can reanimate everything at once, and then these two die right away. Besides, I need Doom Whisperer's type of mill to find and activate Second Chance and I don't have enough removal for artifacts/ench.

Skull Prophet adds mana to get me Muldrotha, and then "mill two cards" is effectively the same thing as "draw two cards". This makes up for the huge mana boost and discard enabling of the apprentice.

Foster is a really good mill card, but Tormod is better.

Torgaar is great against life gain decks, but they aren't very common and Jarad is effective against all decks.

Azusa is good, but she won't let me play more cards from the graveyard and Kodama of the East Tree lets me put lands from my hand into play whenever I put anything into play. I need the lab maniac for the Zegana win condition.