Yawgmoth, Thran Physician (EDH / Commander)

Yawgmoth, Thran Physician

This is a relatively budget wise build that I believe affects Yawgmoth's value engine at full force.
Our goal is to draw many cards and remove/cripple opponents' creatures by sacrificing your own and distributing -1/-1 counters on theirs.
By drawing many cards and controlling your opponents, you will find one of several winning synergies, resulting in a group slug.
This deck is best described as a group-slug, aristocrats, control deck.
Let's dig in.

What We Are Leaving Out...

Our build does not interest itself with infect at all. Though this is a valid strategy, I fear that it would be too alarming to our opponents and not as fun as the group slug route.
The build largely ignores proliferation as well, except for the ability on Yawgmoth himself, but we mainly use this as a discard outlet, and we have a few cards that will give us a payoff for those discards.
Make no mistake, however, proliferation in this deck is good - just not something we focus on.

In an Ideal World...

In a perfect game, we would have Yawgmoth, Thran Physician, Zulaport Cutthroat, Nest of Scarabs, and Geralf's Messenger on board.
Pay 1 life, sacrifice Geralf's Messenger (triggering Zulaport Cutthroat, making up for our paid life and draining our opponents), and place a -1/-1 counter on a opponent's creature (triggering Nest of Scarabs, creating a 1/1 Scarab token).
When Geralf's Messenger dies without a +1/+1 counter, he returns to the battlefield with one, dealing two damage to an opponent.
Pay 1 life, sacrifice the Scarab (triggering Zulaport Cutthroat, making up for our paid life and draining our opponents), and place a -1/-1 counter on Geralf's Messenger, removing his +1/+1 counter.
Now we are back where we started: Yawgmoth, Thran Physician, Zulaport Cutthroat, Nest of Scarabs, and Geralf's Messenger (without a counter) on board, and we can repeat this process infinitely, draining the whole table.
Because we drain each opponent for 2 every time we execute this loop and another opponent for an additional 2, it would take 18 repetitions to kill our opponents in a game in which they all have 40 life and we have greater than 1 life.

In the Real World...

It is highly unlikely in my estimation that we will be able to reach that perfect scenario reliably and avoid disruption if we do; however, this synergy can be exploited in finite ways that are better understood by removing certain cards from the equation.
Let's remove Zulaport Cutthroat (or another aristocrat) from the equation. Yawgmoth, Thran Physician, Nest of Scarabs, and Geralf's Messenger are on the board. With these, we can basically kill ourselves and another player because we lose the life-gain. However, this is a perfectly valid temporary strategy that will help us draw in to an aristocrat - hopefully, Zulaport Cutthroat.
Let's remove Nest of Scarabs from the equation. Yawgmoth, Thran Physician, Zulaport Cutthroat, and Geralf's Messenger are on the board. All we have lost is the infinitude of our engine, but we can still repeat the loop as many times as we have a tangential creature to sacrifice. With all our token generators, we should have quite a few, and we may even have enough to draw into some reanimation to call back an enters-the-battlefield token generator to replace our dudes - or we might draw into Nest of Scarabs.
Let's remove Geralf's Messenger from the equation. Yawgmoth, Thran Physician, Zulaport Cutthroat, and Nest of Scarabs are on the board. As long as we have one other creature to start the loop, we can repeat it infinitely. The only catch is that it is much slower. It takes 20 repetitions, and all your opponents die together at the end instead of one by one earlier in the loop.
All of these drawbacks are non-issues, really, because we are getting a ton of value and drawing into their solutions the whole time.
Another thing to consider is how many substitutes we have for each card.
Zulaport Cutthroat has Blood Artist and Vindictive Vampire to fill his role though slower.
Nest of Scarabs has Genesis Chamber.
Geralf's Messenger can be replaced by Mikaeus, the Unhallowed who makes almost all of our creatures into undying dudes that can fuel the loop. This results in a slightly slower kill because they aren't doing 2 every time they come in, but it is a kill none the less.
Diabolic Intent and Dark Petition function as replacements for the best version of whatever we happen to missing.

Alternate Win Conditions...

Just in case we are totally locked out of the loop described above - probably by snipping our commander - we can win a few other ways.
The first and least elegant is a big mana Torment of Hailfire fueled by Magus of the Coffers, Cabal Stronghold, Crypt Ghast, Nirkana Revenant, etc.
The second is Walking Balista and Mikaeus, the Unhollowed. Mikaeus gives the Ballista undying, so when we remove that last counter, the Ballista comes back with another as many times as we want. This works well with an aristocrat as well.
If the game goes long, we can play Gray Merchant of Asphodel to close it out, and if God is willing we can beat someone with their own deck via Praetor's Grasp.