Well, I couldn't help myself, Muldrotha is one of the most played commanders in multiplayer brawl, and I find myself joining the masses. But when it's all said and done, there are some fun mechanics to try with this general and I wanted to tackle him a slightly different way.
This deck has more of a focus on non-permanent cards, for a slightly heavier control element in opponents turns and also broader answers in some sorceries. I was really keen to focus on The Mirari Conjecture as a renewable source of retrieving instants and sorceries. Muldrotha is then able to get it back when it's finished it's Third Saga.
What did I figure out playing Muldrotha in my first iterations?
I'll start off by saying that this posted list is after quite a few versions, certainly trying out a lot of cards and strategies. It's almost easier to explain what's not in the deck.
When I was looking at this legend mainly for commander when it first came out, I was really thinking about getting an even distribution of permanent types, so that you could get maximum value each turn, bringing back an artifact, creature, enchantment and even possibly a planeswalker, every turn.
This might be fine for commander, with it's numerous fast mana, and cheap value permanents.
However, what I found in Brawl is that you can just never have enough mana to cast everything that you have access to with Muldrotha. With virtual hand sizes spanning your graveyard, you will never have enough mana to cast absolutely everything you would like. Can't really complain, boo hoo too many cards, but it does put into perspective that in reality, you will only be casting one or maybe two cards a turn from your graveyard, and even then this is in the later stages. So with my configuration I've settled on quality of singular cards, rather than value on trying to get a permanent of each type, each turn, as this is not really possible.
With this in mind, I have a heavy bias towards enchantments, being powerful and fewer answers for removing them in the format. The deck doesn't have many artifacts, is creature light, and has no planeswalkers.
The deck is relatively creature light, as it packs mass-creature removal.
This deck is designed to grind your opponents out of resources. You want to drag them into deep waters, testing their ability to hold off from continuous removal. It does have a big wind-up period, so you will take a lot of heat during the beginning and middle parts of the game. Muldrotha is no surprise to opponents, don't expect them to be easy on you, as they know how hard it is once you get into the later stages of the game.
Graveyard hosers, the hate is real
What you will come to expect is that you'll come up against graveyard hate a lot, and it becomes a sort of sub-game within the game. Trying to navigate around these, finding answers, not get blown out as much as you can. This is just part of the territory, if you were always allowed to have virtual hand size of 20, then the game would degenerate too quickly. So although it is hard to play against, it is part of the game, and you try to configure your deck to not be completely dead to popular graveyard hate cards. This is what I've done to a large extent, and I will explain card choices in the following sections.
The deck is centered around control, there are very few outright win conditions. As I mentioned there is a focus on The Mirari Conjecture as a means of getting some of your more powerful instants and sorceries back again and again.
Disallow and Negate are key cards in the deck for stopping some of your opponents more powerful plays. In general we are looking to get one of these back with The Mirari Conjecture. Bontu's Last Reckoning, Yahenni's Expertise, River's Rebuke are sorceries you will be potentially looking to return, and really set your opponents back, allowing you the room to setup even further. With The Mirari Conjecture ability to copy effects, you can often target two opponents with River's Rebuke. Once this is done, you can start the cycle again, recast The Mirari Conjecture getting back a counterspell as the first step, then look to do exactly the same with mass removal over the next couple of turns, bouncing all your opponents cards back to hand, or destroying all the creatures.
You can literally grind your opponents out of relevant threats or ways to deploy them in a timely manner,
Phyrexian Scriptures is an enchantment that can destroy all creatures (except Muldrotha of course), and this is another lock cycle that is hard for your opponents to overcome.
Further to this Ravenous Chupacabra, Banewhip Punisher, Hostage Taker, Noxious Gearhulk, can be cast potentially every turn to remove the biggest threats from the board. If your opponents are not attacking into these creatures, with their own creatures, then it normally means that your life total is remaining intact. It's tempting to run a creature sacrifice outlet, but I've found that blocking is a reliable way of getting creatures into your graveyard. It's a case of your opponents are damned if they do, damned if they don't attack/block.
In Bolas's Clutches and Lay Claim are expensive, and more for late game, but really provide inevitable on what your opponents can really do. You can think of these as the win conditions for the deck. Once your opponents can't really play anything out that's relevant without it being stolen, it only a case of going through the motions to close the games.
As I mentioned, you can just never have enough mana in this deck. With your graveyard being a virtual extension of your hand, there is simply not enough ways to produce mana in the deck to cover all the cost of what you'd like to do.
There are numerous mana accelerates, with land ramp and some artifact mana. It must be noted that my first versions had little additional mana sources, however this was soon realized to be a mistake. Other decks might run mana creatures, however this deck has some powerful creature removal cards, so no point running into these.
So with realistically only casting one, maybe two spells a turn from your graveyard, we have some cheaper utility creatures that provide value. Certainly not unhappy for them to die, as you can recast them later on.
The land base is mostly basics, as you will filter through, most likely all of them once you get a foot hold with the deck. My earlier versions and a lot of "cute" non-basics, however I found that I was never using their abilites (mana hungry deck, never time to activate them), and that I was constantly running out of basics to search for in the deck. Field of Ruin and Evolving Wilds are the two best lands in the deck for getting renewable value from Muldrotha, and often I get both these cards with Hour of Promise.
Once you get one of these cards going with Muldrotha, then you will draw excess lands during the course of the game.
Drawing cards is not really needed at all for this deck. I do have Unbridled Growth as a cheap way of getting some card draw value, but often you're not looking for additional draw, noticeably trying to maximize what you have in your graveyard to make sure you get value before some potential graveyard removal.
Without a doubt the best graveyard setup card is Perpetual Timepiece. Search for Azcanta is also excellent, and often I don't transform it, as most people are running Field of Ruin and I find I just like to get the filtering value anyway.
On that note, I do have Journey to Eternity and the transform land Atzal, Cave of Eternity is potentially amazing, but I do find that you shouldn't expect it to sit around for long, as it's a must be dealt with by opposing land removal. But it is still nice insurance, being able to put it onto Muldrotha, so it makes it hard for your opponents remove him.
Hope of Ghirapur is the only natural sacrifice artifact, and this can be used to lock down a particular opponent, if you feel they have powerful non-creature spells (there is always one).
Mirage Mirror is in my opinion, the best general utility card in Brawl. I'm a believer. It's almost impossible to remove if you have mana available. You can always make it a land in the face of removal. It's really saved me in a lot of games, making it hard for opponents to attack into it, as you can make it the largest creature on the board. Even if does go to graveyard, you can recast it again with Muldrotha. I could go on for days about this card..
Karn's Temporal Sundering is a little usually in a Muldrotha deck, but the ability to break even a little further ahead with card advantage, makes this card worthwhile, even if it is a dead card during the first stages of the game. If you copy it with the Third Saga of The Mirari Conjecture, then you can recast The Mirari Conjecture getting back your counterspell, then on the second extra turn get your sorcery mass removal, you get the idea..
First of all don't be greedy. If you have the ability to fill your graveyard, really assess if what you have already in the yard is enough to provide the traction you need to go to the late game. It's tempting to just keep filling it up with Perpetual Timepiece or Search for Azcanta, but sometimes it's just better to make do with what you have. This will better prevent from getting blown out by one of these hosers.
Also you might have more powerful cards in hand, but try and stretch out what you have in the yard already, even if the plays are less powerful. Same deal, makes sure that you get maximum value before they are potentially removed.
The deck does pack a lot of removal however, so as long as you are patient, you do have numerous answers for these cards: Naturalize and Slice in Twain are universal instants. I found that I wanted to have a threshold of instants for the The Mirari Conjecture, so ones that can remove graveyard hate is nice for the deck.
Nimble Obstructionist can be used directly to stop Scavenger Grounds or other activated ability that removes graveyards. It is one of the weaker cards in the deck, holding up the mana and holding in your hand does come at a price, but a necessary evil for part of the sub-game you have to play. Disallow also allows you to nullify one of these effect if already on the board.
Avoid using cards that further reference the graveyard. It's tempting to run additional powerful cards like The Scarab God, Yawgmoth's Vile Offering or say The Eldest Reborn. However I feel this is a bit of a trap, leading to additional cards that can be stopped by the same strategy that is already holding you up.