How BG Yawg Works In Modern MtG

I won't be explaining the rules of Magic the Gathering super in depth here, just explaining what's needed as I go. This may need a few revisions for clarity. As a reference, I'll be using this relatively old list (the deck is surprisingly fluid), as the main board has just about every relevant card that interacts with the combo. Just know that one of those cards (Geralf's Messenger) no longer sees play in the list for reasons I'll elaborate on. I should also say here that "Modern" isn't, like, an "era" of Magic- it's a format. The card pool for Modern is every Standard legal set starting from 8th Edition, plus Modern Horizons 1, Modern Horizons 2, and the LotR set. Other than that, it operates by the normal rules of Magic.

BG Yawg is a combo deck that's about as old as the namesake card itself- Yawgmoth, Thran Physician. The deck itself focuses heavily on creature utility; with the exception of the creature tutors, every spell in the main board is a creature (including Grist, thanks to her passive). The main goal is to develop a wide board, play out Yawgmoth, and control your opponent's board before winning with one of multiple infinite outlets. The backup plan is to just beat face with Undying creatures ("When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield with a +1/+1 counter'); they're much stronger than you would expect. The deck itself is one of the more difficult decks in the format, but I'm also of the opinion that it's one of the most well designed decks in the game.

As stated before, the deck mostly wants to make use of Yawgmoth to secure wins, mainly through his first ability: sacrificing creatures to draw through your deck and/or distribute -1/-1 counters. The "generic" combo with Yawgmoth involved 2 Undying creatures, and relies on the interaction between +1/+1 and -1/-1 counters. If a creature has a +1/+1 counter, and a -1/-1 counter is placed on it, then both counters are removed (and vice-versa). So if you have two Undying creatures, if one has a +1/+1 counter on it, you can sacrifice the other with Yawgmoth, targeting the first Undying creature. This triggers Undying on the sacrificed creature, bringing it back with a +1/+1 counter, which resolves first. Then, the activated ability resolves, removing the +1/+1 counter on the first Undying creature (the one not sacrificed) and drawing a card. The obvious complication is that this isn't infinite- each loop costs 1 life, meaning you'll eventually lose unless you draw into (or already have) a way to close out the game. There are 4 cards that the deck can generally play to enchance the combo- the first, Prosperous Innkeeper, does not win the game by itself, but lets you draw for as long as you want, as the lifegain negates the life loss. The other three cards are:

• Hapatra, Vizier of Poisons. While maybe wrong to list her here, as she can also function as an Undying creature in the combo (you just sacrifice her snakes instead of her), she is mainly in the deck as a win condition. The use case for her is pretty obvious: make a big board of snakes that either lock down the board or go in and kill the opponent. With Innkeeper in play, she also serves as a way to gain infinite life, as each loop would now cost 1 life but gain you 2. She was actually removed from the deck for a while, but was eventually brought back as the meta shifted and favored the deck running wider board states and less dorks.
• Blood Artist This one is probably pretty obvious: now instead of you losing one life each loop, your opponent does! Generally when you're going for a combo kill, this guy is the one you wanna get into play for it. An alternative in this slot is Zulaport Cutthroat, not for the 1 power but for not targeting, getting around hexproof and protection. In general though, it's better to play Blood Artist even with other decks playing ways to gain hexproof, as most hexproof effects are one-shot effects that you can just wait out, and Blood Artist triggering on every creature dying (not just your own) makes it much stronger if you wind up having to play it outside of a combo turn, such as in the mirror. Or if you wind up in a topdeck war or something.
• Geralf's Messenger. This card used to be the only combo outlet in the deck. It used to be a playset. This is despite how the card actually messes with the deck in many ways. Even when it was playable, Geralf's Messenger was always the worst card in the deck, for really just one reason- the mana cost. The card itself is a reasonably strong threat when played on its own, but costing BBB is really, really bad, as the deck is actually primarily green. This basically forced the deck to run a lot of mana dorks (1 mana creatures that can tap to add mana), and to play Urborg, Tomb of Yawgmoth, just so it wasn't a completely dead card if you happened to draw it. Eventually, however, the deck shifted, cutting one or two Birds of Paradise due to the large amount of cheap removal in the meta, and cutting the last remanining Messenger for Hapatra. I guess to talk about how the card actually worked, the way it interacted with the combo was also probably the worst of all the cards listed here. By including it as one of the creatures in the loop, you would deal 2 to your opponent every other loop- or, to put it another way, you would have the lose life at the same rate as you. This partially added to how hard the deck is, as it meant you had to be more conservative with your life than usual, due to one of your combos being reliant on your life total (and life in general representing cards). Without Messenger, while you still need to be careful with your life, you can afford to take more damage than you could before, as you have other ways to close out the game.

I should also mention that it's pretty fortunate that the deck even exists, due to just how rare Undying is. Undying as a mechanic has now only shown up twice, but in just two small sets- and not as a main theme in either. There are only 18 creatures with Undying, and most are either red, expensive, really bad, or some combination of the three. If Geist was never printed, the deck would have to use the much weaker Butcher Ghoul; if Young Wolf was never printed, I'm not sure if the deck would even be viable at all. The fact that the deck exists thanks to random limited cards is honestly part of the charm for me- and not only are they random limited cards, they're legitimately good! Undying is actually a very strong mechanic, and being able to play beatdown with hard-to-kill creatures if you don't draw into a combo outlet is a genuine strength of the deck. Not only is there a good plan B, but you can easily transition from that plan B to the main combo plan.