He'll cure what ails ya!
This is my personal Yawgmoth list, and it has slowly shifted from graveyard value and shenanigans to fast, versatile, and resilient combo. There's a few main combos in the deck that you can use to kill on the spot, and for the most part they can all be executed at instant speed. This will not be an exhaustive list of every combo here as there so are so many moving pieces in the list, however these are the main few that I tend to default to.
The easiest combo to pull off that works at instant speed is Mikaeus, the Unhallowed + Walking Ballista. With these two you can shoot down the whole table, and if you have an additional sac outlet in play, you can also get around removal. Also, if you have a sac outlet or other effect that you can use to generate mana, you can also get infinite mana, like with Phyrexian Altar, Pawn of Ulamog, or similar effects. This is a very easy combo to default to because it's two cards, does not rely on the commander, and can be pushed out very quickly by using cards like Buried Alive and Victimize.
The next combo is another easy combo that also plays well with the other combos, this doesn't kill on the spot, but if you add a few pieces it absolutely can. For this you need Gravecrawler and Phyrexian Altar and any other zombie in play. With this you can sacrifice Gravecrawler to the altar for a black mana, then recast it from graveyard immediately. With this you get infinite storm (and gravestorm for Bitter Ordeal), infinite dies triggers, infinite ETB, and infinite leaves the graveyard triggers (for Syr Konrad, the Grim. If you add in Blood Artist you can now kill the whole table and gain infinite life, and with Pawn of Ulamog or Pitiless Plunderer you have infinite mana.
This next combo gets a little complicated but it absolutely works, as each piece is good on its own, but when all are together you can kill the table. K'rrik, Son of Yawgmoth + Chainer, Dementia Master + Gray Merchant of Asphodel + any sac outlet is an easy way to both gain a lot of life but to also kill the table after only a few activations. By using K'rrik to pay six life instead of BBB for chainer, you can effectively pay nine life to put any creature card from any graveyard into play under your control at instant speed. Using this in conjunction with Gray Merchant of Asphodel and a sac outlet, you can recur gray merchant for as many times as you have nine life to pay. The reason I use gray merchant here is that when it ETBs, your devotion will be minimum seven, and if you have 3 opponents you're going to be gaining 21, which is another two activations of chainer. With more black pips in play, this drain gets much larger and can be done infinitely to kill your opponents, provided you have a way to kill your gray merchant in between activations.
You can also use Yawgmoth, Thran Physician + Mikaeus, the Unhallowed + Blood Artist + any other non-human creature to kill the table. By sacrificing Blood Artist to Yawgmoth, you will be even on life, up one card, and you will have drained your opponents for one each. Blood Artist will then come back to the battlefield with a +1/+1 counter on it due to Mikaeus granting it undying. You can then sacrifice your other non-human creature to Yawgmoth to place a -1/-1 counter on Blood Artist, which will cancel out the +1/+1 counter, leaving it back at its original state. The second creature will then return to play with a +1/+1 counter on it as well, and at this point you can then sacrifice the Blood Artist again, but this time putting the -1/-1 counter on your other creature, so the counters will cancel out and it can then undie again. Now you can demonstrate a loop by which you alternate between sacrificing these two creatures to get infinite card draw, dies triggers, and ETB triggers.
There are a few other combos that exist in the deck, but don't necessarily win. Yawgmoth, Thran Physician + Nest of Scarabs + Blood Artist allows you to both draw a bunch of cards out of your deck and also kill any of your opponents creatures that you can target. By sacrificing any creature to Yawgmoth with Nest of Scarabs in play, then placing a -1/-1 counter on any creature, you will get a 1/1 black insect token. You can then sacrifice the insect token to Yawgmoth, place another -1/-1 counter on a creature, getting you another insect, and with blood artist keeping you alive you will also drain your opponents for one each time. This is a good way to control the board and prevent your opponents from having too many creatures, or at least shrink them if you need to. This will also draw you a card for each creature you sacrifice, so you can also utilize this combo to place counters on your own creatures, leaving them at one toughness, to draw through your deck if you need to.
The nicest thing about this deck is that all the pieces in it play very well together, and often times I find myself accidentally finding a win through one or more of these combos, and with the amount of recursion the deck has, you can pretty easily fight through your creatures dying. One good example of this is Agadeem's Awakening
. By paying 7 mana into X, you can get back K'rrik, Son of Yawgmoth, Mikaeus, the Unhallowed, Chainer, Dementia Master, a 4 drop creature, a 3 drop creature, Blood Artist, Gravecrawler, and Walking Ballista. For 10 mana, which in this deck isn't too hard to get to, you can bring back two different combo lines at once, with 2 open slots for any other creatures that may be in your graveyard. The biggest upside to this card is that on the reverse side, it's an untapped land that taps for black, which is great because it's not only a combo piece, but a land at the same time.
Another good synergy within the deck is Bolas's Citadel & Necropotence. You're able to not only cast cards off the top of your library with Bolas's Citadel, but you can also play lands, which can be good if you haven't made a land drop this turn. However, if you have already played a land and there's one on the top of your library, you can pay 1 life to Necropotence to exile that card, allowing you to see the next card on top. This is useful because you don't need to have Yawgmoth in play to be able to draw cards to get past lands on top, but even beyond this, you can use it to exile cards you may not need or want. For example, if you have Citadel and Necropotence in play, and a reanimation spell on top, but no creatures to target, you can simply pay 1 life to exile it and see the next cards. This allows you to be very selective with what cards you cast of the top and which you don't, and in the event that either card gets removed, the other is still a potent value engine.
Overall, this deck has a lot of potential to it and I love playing it, with cards like Bolas's Citadel, Vilis, Broker of Blood, Necropotence, and Ad Nauseam , you can easily draw a lot of cards very early to get your combo pieces in hand, then by using cards like Songs of the Damned, Culling the Weak, Cabal Ritual, Bubbling Muck, and Rain of Filth, you can cast these cards much earlier than otherwise possible in order to push out a win very quickly. But if your combo is interrupted or otherwise stopped, you can come back later and try again by bringing your creatures back using Reanimate, Dance of the Dead, Necromancy, Dread Return, Living Death, Victimize, Unearth, Shallow Grave, and Corpse Dance. Overall, the deck is very potent and can do some serious damage if left unchecked, but even if pressure is applied, you can still come out on top.
