Karumonix, the Rat King Commander Deck Guide

Last updated on April 26, 2023

Karumonix, the Rat King | Illustration by Helge C. Balzer

Rats are a controversial creature, to say the least. Traditional carriers of plague and disease, they make their homes in the dark, dank places of the world and wallow in pestilence and scum. Contemporarily, they make cute house pets!

The rats in this Karumonix, the Rat King Commander deck aren’t the affectionate type. They’ll sicken your opponents with poison counters all while nibbling at their cards in hand to keep them from executing their own win conditions.

What are the best rats for a poison counter deck? And what are the best ways to support them? Let’s head down to the sewers and go rat hunting!

The Deck

Typhoid Rats | Illustration by Dave Kendall

This Karumonix, the Rat King deck is more than just a simple rat tribal deck with a toxic commander slapped on top. Karumonix’s poisonous lord effect is its greatest upside, to be sure, but its ETB effect isn’t a one-and-done.

We’ve seen with Gonti, Lord of Luxury decks that bouncing a commander in mono-black isn’t as hard as it appears, so this deck looks to use pseudo-flicker spells to continually use Karumonix’s triggered ability. Any good poison deck also needs some proliferation, so I’ve included a good deal of it.

The Commander

Why choose Karumonix, the Rat King over other rat legendaries? Marrow-Gnawer dominated the rat tribe for years with a great evasion anthem and a token generation effect so fast we haven’t seen anything like it since Krenko, Mob Boss. Where Marrow-Gnawer falls short is its comparatively steep mana cost, which can be costly in a tribe with traditionally low-mana value creatures. Marrow requires other spells or effects to keep generating rats, while Karumonix’s built-in triggered ability digs for more rats instantly.

Ink-Eyes, Servant of Oni and Nashi, Moon Sage's Scion are both good cards but can’t use their ninjutsu abilities from the command zone. Ashcoat of the Shadow Swarm is probably the only real competition Karumonix has, and it might be better depending on your particular rat build. But when it comes to poison counters, Karumonix is the (rat) king.

Here’s the final word on Karumonix: it’s just plain cheaper than any other legendary rat (technically Greasefang, Okiba Boss is also three mana, but it’s clearly a vehicle-tribal commander, not a rat one). Commanders with low mana value hit the field sooner and start synergizing with their creatures sooner. Your rats won’t poison opponents without Karumonix on the field, so sticking it to the field early is essential to making this deck run.

Ah, Rats!

Every rat deck needs a swarm of tiny bodies rushing around your ankles, scavenging for edible garbage, and scurrying behind shelves and under refrigerators. These rats fall into a few broad categories: toxic and infect rats, Pack Rats, rats with evasion, and the classic discard rats.

Doubling down on the toxic and infect rats is a no-brainer for this deck, but remember that Karumonix, the Rat King’s toxic anthem stacks with other sources of poison. That means that Blightbelly Rat gives two poison counters, and Ichor Rats and Septic Rats generate three poison each when they connect with an opponent.

This deck also runs a handful of Pack Rat-like creatures that check the number of rats you control to determine their power, toughness, or both. Pestilence Rats and Swarm of Rats are your back-up Pack Rats. While they’re definitely downgrades, they both make good targets for Phyresis and Glistening Oil.

Despite attacking every turn with your rats, you’re not looking to win via combat damage; you’re just trying to connect with your rats to generate poison counters. Your best rat with built-in evasion is Marrow-Gnawer, who also passes the fear mechanic out to every other rat you control. That alone is enough to end a game if you have enough rats on the board. If you don’t, Marrow-Gnawer can pump out an exponentially increasing number of rats every turn.

Besides the obvious powerhouse that is Marrow-Gnawer, I want to shout-out Rancid Rats, Sinuous Vermin, and Stronghold Rats. These nasty little guys come with their own evasion, letting you spread poison counters around without any extra support.

Cheap rats commonly make use of discard effects; it’s sort of their “thing.” Burglar Rat and Rancid Rats are your go-tos, with Drainpipe Vermin as a slightly-slower option. Chittering Rats’s pseudo-discard effect is actually better than a standard one since it locks an opponent’s draw on the following turn. It’s also your only play against those pesky madness and cycling decks that actually want to discard cards.

In a similar vein you’ve got some of the original Kamigawa block’s hand-size manipulators. Gnat Miser and Locust Miser have punishing static effects, at least until someone hits their Reliquary Tower or Folio of Fancies.

There are also a handful of rats present that are uncategorized. Crypt Rats is a weird potential sweeper that really wants to be enchanted with Phyresis.

Kuro's Taken is just a generic rat with a regenerate ability, so you can swing in with it each turn without worrying about it dying.

Typhoid Rats is a cheap rattlesnake in the early game, and an unappealing block target later on.

Vermin Lords

You’d think a rat tribal deck wouldn’t want to run any non-rat creatures, right? Wrong! There are four non-rats in this deck, and each is essential to running this tribe.

Ogres have an affinity for rats (Ravnican ogres, at least), and these are epitomized in Ogre Slumlord and Ratcatcher. The Slumlord keeps your board full of rats while also disincentivizing blockers by guaranteeing a trade-up when your deathtouch rats do combat with their creatures. Ratcatcher, on the other hand, is an amazing repeatable tutor on a body that’ll shake off a Lightning Bolt.

Your two humans are both warlocks. Piper of the Swarm has another evasion anthem in the form of menace added to a token generation effect and an exciting way to steal creatures from foes. It's an effective way to grab an actually threatening creature to protect your board since most of your rats are comparatively puny.

Chittering Witch comes from the Forgotten Realms Commander precons, and it's undoubtedly a “Commander card.” Hopefully you’ll see all three Rat tokens when it comes down, but don’t expect that activated ability to destroy much without some support.

Gettin’ Around

Playing a ton of rats and giving them toxic 1 is useless until you find a way to get around your opponents’ blockers. I’ve already mentioned some of the naturally evasive rats and your #1 best rat Marrow-Gnawer, but that’s not all you have.

Cover of Darkness is probably the most important card in this deck, granting fear to your entire board but for cheaper than Marrow-Gnawer, and on an enchantment.

Aside those two spells, Rogue's Passage and Access Tunnel can sneak at least one rat past a blocker.

An Endless Swarm

You want to swing in with every rat every turn (including Karumonix, the Rat King), but their weak power and toughness means they often won’t survive combat. Luckily, black has the most access to reanimation effects.

Dread Return and Blood for Bones can grab that single Marrow-Gnawer you lost to removal, and they’re one mana cheaper than paying for a commander-taxed Karumonix. For one more mana you can cast Vat Emergence and proliferate your poison counters for your trouble.

Patriarch's Bidding is the best way to get every rat back onto the battlefield, but it’ll be punishing against another tribal deck. It's best saved for the late-game when you can return five or more rats at once.

Haunted One grants a non-keyworded undying effect to your whole board whenever Karumonix swings in. Read that again. You’re getting a Mikaeus, the Unhallowed anthem for three mana, with a power bonus on a harder-to-remove permanent. Perfect tribal card, no notes.

You’ve got your Whip of Erebos in case you run out of single-use reanimators. While the lifelink anthem won’t be as effective across a board of power 1 and 2 creatures, that incremental lifegain shouldn’t be discounted.

Creeping Corruption

Karumonix can’t be your only source for poison, so let's consider some alternate ways to infect your opponents.

Granting infect to non-toxic creatures can turn your Pack Rats and others into huge threats, so Glistening Oil and its common sibling Phyresis can be slapped onto just about any creature in this deck for great effect, but the bigger the better.

Sometimes you just won’t be able to break through your opponents’ stax effects (too many Aura of Silences and Propagandas running around these days). Luckily you won’t have to. Once you’re in for even one poison counter on an opponent you can just use your host of proliferate effects to tick them up to a loss.

I’ve replaced most of the run-of-the-mill interaction spells with their proliferating alternatives. Spread the Sickness and Whisper of the Dross sub in for a typical Murder, Infectious Inquiry appears instead of Sign in Blood, and Phyresis Outbreak (not technically proliferate, but it’s the same outcome) takes the spot of a Mutilate or Crippling Fear.

Let’s round out this section with Contagion Clasp and Karn's Bastion and call it good.

Tribal Synergy

Of course you need some cards that actually interact with your creatures’ types in any “creature type matters” deck. I’ve already touched on Haunted One, but no tribal deck is complete without one of the many generic tribal artifacts.

This deck runs Icon of Ancestry rather than Coat of Arms or Door of Destinies, because you don’t care about how big your rats can become. What you really need in this deck is a consistent way to dig for more rats when others inevitably die. They’re just not worth the investment to power-up when you’re only looking to trigger their toxic effects, not necessarily the combat damage.

The Joys of Playing Mono-Black

It seems a lot of mono-black decks use the same or similar generic value generators, and for good reason. Cards like Read the Bones and Skullclamp are great in any deck, but I’ve included a few rat-specific engines.

Tribute to Horobi is a great 2-drop. You’ll have at least six Rat tokens ready to turn into card draw once it transforms. This only gets better once you find your Dark Prophecy.

Speaking of Rat tokens, let me introduce you to Plague of Vermin. Sure, you might give the lifegain player 100 Rats for free, but their Rats are nothing compared to your infectious little guys.

The Mana Base

Mono-black mana bases are easy to build: just run black lands. A majority of your spells are three mana or less, so you’re running 34 lands and three extra mana rocks: Sol Ring, Arcane Signet, and Glistening Sphere.

As far as ramp goes, mono-color decks benefit greatly from Caged Sun, and I always try to find room for Jet Medallion if possible. And Cabal Coffers is here too just to be completely sure you don’t run out of mana.

Don’t underestimate a Dark Ritual in EDH, either. A turn 1 Karumonix is three times as threatening as one on turn 3.

The Strategy

Karumonix, the Rat King wants to do one thing, and that’s attack with rats. You’ll build a board of rats and then drop Karumonix and some evasion to overwhelm your opponents before they know what hit them.

You can afford to keep a hand with just three lands in this deck, and maybe even as low as two if you’ve got access to another form of ramp. I’d make sure you have access to at least two black mana so you don’t miss the Karumonix cast on turn 3.

Your early and mid-game plays look very similar. Gradually play your innocuous-seeming Drainpipe Vermin and Ravenous Rats, and then refill your hand with Karumonix’s ETB effect. You’ll want to use your tutors to find either Marrow-Gnawer or Cover of Darkness ASAP. If you’ve already pulled them fetch up Piper of the Swarm as extra insurance, or a Pack Rat to start going as wide as possible.

You typically won’t win a game with one big swing, suddenly taking everyone to 10 poison counters at the same time. It’ll be a slow burn, gradually bringing your opponents to 10 as they fret about their life totals and do combat with each other. A surprise proliferation effect from Contagion Clasp or Whisper of the Dross can seal the deal, but don’t expect this deck to win like Craterhoof Behemoth.

Combos and Interactions

This deck runs no infinite combos! That feels like an accomplishment considering the current Commander environment. There are, however, some interesting poison counter interactions to clarify.

First, remember that granting an already-toxic creature toxic 1 from Karumonix means it’ll give an opponent a number of poison counters equal to its total toxic value, so Blightbelly Rat actually connects for two poison counters with Karumonix on the field.

The next is that infect references all damage, not just combat damage, so slapping Phyresis or Glistening Oil on Infected Vermin or Crypt Rats can be a great way to sneak poison counters past heavily-defended battlefields.

Rule 0 Violations Check

I can’t think of any glaringly obvious Rule 0 violations this deck might have. I guess some folks are still salty about poison counters even getting support, but you don’t have to play with those people.

Budget Options

This Karumonix, the Rat King Commander deck comes in at just shy of $250. That’s a fair start for a deck, but let’s take a look at some upgrades and downgrades to adjust that price.

Cheaper

There are more than a few $20+ cards in this deck, so they’re first on the chopping block.

Marrow-Gnawer, while amazing, isn’t required to run a successful Karumonix deck. Swap it and Cover of Darkness out for some generic fear and menace-causing spells like Aphotic Wisps or Dance of Shadows.

Or you can ditch the Cabal Coffers and Jet Medallion to focus on cheaper mana ramp like Commander's Sphere.

More Expensive

Maybe you’ve already got a Marrow-Gnawer and a Cover of Darkness. What’s next for this deck, then? Why, Ashcoat of the Shadow Swarm, of course!

Ashcoat is probably the best reanimator you could include in this deck, and it makes a great swap-in for any of your single-use reanimators, like Blood for Bones.

Other Builds

Karumonix, the Rat King clearly lends itself to a poison counters build. But this doesn’t need to be the be-all, end-all of rat decks.

For example, why bother with all these different rat creatures when you could just run 30 copies of Rat Colony? Pick up Thrumming Stone and you’ll be skittering and swarming in no time.

Alternatively, rat decks can double-down on the discard mechanics. Many of them share and run cards like Liliana's Caress and Megrim to further punish other players when your rats hit the field.

Commanding Conclusion

Pack Rat (Return to Ravnica) | Illustration by Kev Walker

Rats have never been the most popular creature type, with a smattering of tribal support and a brief moment in the sun during the Kamigawa block. Karumonix, the Rat King looks to change that.

Karumonix captures the theme of rats being disgusting, disease-ridden creatures and rewards players for playing a lot of little bastards. It offers a fun deckbuilding challenge to craft a deck with just the right amount of evasion effects while still maintaining that rat theme. I expect Karumonix to become the most popular rat commander in no time, and maybe one of the most popular poison counter commanders too.

What do you think? Will you be torturing your playgroup with a poisonous deck? Are there any better ways to sneak your rats past blockers besides Cover of Darkness and Marrow-Gnawer? Let me know in the comments or over on Draftsim's Twitter.

Thanks for reading, and watch where you step!