Underworld Breach is going to make waves in every format in which it remains legal.
It is sort of like a mix of Past in Flames and Yawgmoth’s Will, with a lighter mana cost than either one at the cost of requiring a deeper pit of graveyard cards to escape away. Trading one resource requirement for another may open up new vistas of deckbuilding, especially in formats that can turn cards into mana, mana into cards, and cards in the library into cards in the graveyard. The more efficient the resource exchange, the better Underworld Breach becomes.
Of course, there is a bit of a difference between the levels of brokenness achievable in the different major formats, as Underworld Breach benefits as the average converted mana cost of a deck drops and as the amount of cheap ways to fill a graveyard increases.
It scales in power with the format, and the older ones are way, way more degenerate than Standard or Pioneer.
For Pioneer, Underworld Breach is probably playable in a narrow combo deck, likely involving Emry, Lurker of the Loch and Mox Amber. By casting Emry, you can mill four cards to feed your Underworld Breach, and Mox Amber is castable from the graveyard. Add in a Diligent Excavator or two, and loops start to emerge where you can mill yourself out and eventually win with Jace, Wielder of Mysteries.
With Teferi, Time Raveler in your deck, you can even cast Underworld Breach, cast Teferi at the cost of three cards in the graveyard, bounce your own Breach, and be ready to run it back later. That pseudo-fair way to present a repeat protection piece for a subsequent combo turn is worth looking at, and it’s even possible that a Jeskai Ascendancy Underworld Breach deck is in the cards somewhere.
There’s some excitement to be found in an engine deck with Underworld Breach, sort of like the Kethis Combo deck that took Core Set 2020 Standard by storm at the end of last summer.
It’s also possible that a deck similar to Lotus Field exists with Breach, leveraging the narrow Chronic Flooding with Hidden Strings, but the weak nature of the other pieces kind of sours the whole enterprise. Better to stick with cards that are at least a little powerful on their own.
My personal first pick for Breach in Pioneer is with Jeskai, with a very rough sketch for a list as follows:
Jeskai Ascendancy Combo was a flash-in-the-pan deck from many years ago, one that exploited the ability of Jeskai Ascendancy to boost large squads of tokens while churning through a deck, but in adding the Retraction Helix + Springleaf Drum piece to the puzzle, a full-fledged combo engine appears. It was Harlan Firer who played a deck quite similar to this one at an Open over five years ago, and it seems like the right time to attempt to make something similar happen again in Pioneer.
Monastery Mentor is just a powerful creature on its own, and as it’s harder to turn on Fatal Push’s Revolt in this format, there’s a decent chance we can untap with it and start doing crazy stuff. The whole deck is quite resilient to Fatal Push, which is a blessing in contemporary Pioneer. Additionally, Teferi works with Underworld Breach in the late-game to spin up a bit of a battlefield straight out of the graveyard.
It’s unclear if there are other, better sideboard plans at our disposal, what with Supreme Verdict; Gideon, Ally of Zendikar; and even Mantis Rider as decent options. But Glorybringer has been well-positioned in Pioneer for quite some time, and it’s sensible to give it a big piece of the sideboard as a divergent threat. It’s also worth looking at adjusting the manabase to include some number of Fabled Passage, as the extra land in the graveyard could be the difference between winning and losing when Breach gets going.
This deck is almost certainly ten cards or more off “ready for prime time,” but it’s a decent place to start when it comes to Underworld Breach. The only thing that sticks out as a missing piece is a bit of lifegain. Maybe Deafening Clarion in concert with a heavily pumped team of tokens? Or perhaps Jeskai Charm. Lightning Helix, where art thou!?
But let’s be frank. Theros Beyond Death already broke Pioneer with Heliod, Sun-Crowned and Walking Ballista. Underworld Breach brings the pain in Modern and Legacy, and the existence of fetchlands is only the first part of it. There are simply more shells where Underworld Breach is exciting, and with more pieces comes a higher breaking point.
There was an awesome Grinding Station combo deck that I was particularly excited about, but Mox Opal just got hit with the banhammer, so that’s a nonstarter now. It’s possible to resurrect it without Mox Opal, but the engine worked best with that fast mana. Perhaps with Emry and Mox Amber, something can still be salvaged.
Previously, once Mox Opal, Grinding Station, and Underworld Breach were together, you could loop Opal as many times as you want, generating a mana each time and exiling the extra cards from Grinding Station sacrifices. Eventually Grapeshot bought home the win.
Now, it’s better to focus on Ascendancy Combo, which is boosted by the ability to use all those dead cantrips and looted-away lands for more gas in the tank. If an opponent destroys or Thoughtseizes your Jeskai Ascendancy the first time, it’s no matter. Just try again with Underworld Breach!
Then there’s the other two-mana red enchantment that enables busted combo turns, our dear old friend Pyromancer Ascension. With Underworld Breach, Ascension lets a player start doing ridiculous things, and it is not unreasonable to expect to mill one’s entire deck before winning with a single Grapeshot or a pile of recursive Lightning Bolts in Game 1.
Unlike the Grinding Station combo deck, this is a normal Storm archetype with the deliberate choice to turn Gifts Ungiven and Past in Flames in for Underworld Breach. Is it worth it to modify the already-successful Gifts Storm deck? Unclear. The deck has less use for excess mana and more need for cards in the graveyard. It gets to play a higher density of maindeck removal in its Lightning Bolts, but also has a harder time against opposing removal spells like Fatal Push and Abrupt Decay. Overall, the head-to-head comparison in the goldfish race is probably about even, but Gifts Storm likely has more play to it against interaction, putting it over the top.
One deck that has subtle flavor associations with this summer’s Hogaak decks, though, is Breach Dredge. With Manamorphose and a chain of Stinkweed Imps or Golgari Thugs, Underworld Breach just freely rips through your deck and finds all the tools you need to win that turn. Generally, this is a Turn 4 combo deck, which may sadly not be fast enough in current Modern, but now that certain bans occurred to slow the pace of the format (particularly Mox Opal), it could be the best thing to be doing.
And of course, the Legacy combo deck of choice seems to revolve around Breach, Lion’s Eye Diamond, and Brain Freeze. With those three cards, one can simply Freeze oneself a few times in a row, generating mana each time with Lion’s Eye Diamond, and then Freeze the opponent for their library after the Storm count is high enough.
It’s unclear if Underworld Breach is better than traditional Sneak and Show, Rakdos Reanimator, or Storm in Legacy, but for now it’s an interesting puzzle to sort out. The relative density of fast mana, cantrips, and protection is hard to optimize!
The best bets for Day 1 of the new format are likely a tuned version of the Pioneer Jeskai Ascendancy Breach deck, or the Modern version with a more all-in combo feel. Remember, the enablers make these decks tick.
But as the graveyard continues to be the most abusable resource in Magic, and nearly a second hand in a wider and wider range of decks, it’s only a matter of time before the proper enabler makes Underworld Breach worth banning.
Regardless of the format or how much Magic has changed in the last twenty years, even a “fixed” Yawgmoth’s Will is always going to be a dangerous piece to add to a format and Underworld Breach is no exception.