An Introduction to Krark and Thrasios in cEDH
I think Rograkh, Son of Rohgahh is likely the strongest commander in cEDH, but I still like to explore alternatives. Krark/Sakashima is one the decks I've been most impressed by and am most scared to play against. The deck is great against tables who aren't familiar with how it works because they might not realize that once both commanders are on the battlefield, it's often too late to do anything about it and they've already won unless they get very unlucky on some early coin flips. At the same time, players who do know but don't want to have to be the one to answer a problem can always tell themselves they have a chance because the coin could save them.
The problem is that if Krark gets killed in response to Sakashima, they can fall pretty far behind, and playing around that can make the deck slow, plus it's vulnerable to some hate cards, like Rule of Law effects.
Why Krark/Thrasios?
Sakashima of a Thousand Faces pairs very well with Krark, the Thumbless because Krark is broken when you get to flip multiple coins on each spell, but Sakashima is the worst card that lets you do that, it's just nice to get it in the command zone. Thrasios, Triton Hero is a better commander with more colors that is more appealing to me compared to partnering Krark with Sakashima.
Krark is still bad without a way to duplicate its trigger, but there are several creatures that do that, and once you're playing green you get more ways to find specific creatures.
Krark also requires a lot of dedication to maximize: Krark/Sakashima has an extremely focused gameplan, while Rograkh/Thrasios is built around flexibility. My attempt to built Krark/Thras is an attempt to combine aspects I like from Krark/Sakashima with the strongest aspects I can preserve from Rograkh's Bouncy House. This means a lot of Krark cards combined with the core creature tutor/Cloudstone Curio engine from Bouncy House.
Why would I do this? What's the advantage of diluting the already very strong Krark/Sakashima deck? There are a few green cards that are incredible with Krark: Manamorphose, Emerald Charm, Crop Rotation, Veil of Summer, Regrowth, and Chatterstorm in particular. These cards add a lot to the strength of Krark. The core creatures for the Bouncy House Cloudstone Curio combos are contained in Izzet and are good with Krark regardless, like Dockside Extortionist, Spellseeker, and Imperial Recruiter; it's just that adding Neoform and Finale of Devastation for Spellseeker to find makes the combo a lot more flexible and easier to assemble.
What Does This Deck Look Like?
Let's start with the most familiar parts to people who know my work, which is the stuff I've ported over from Rograkh's Bouncy House:
First, I'm still playing all the cEDH staples that would require more explanation not to play than explanation for their inclusion:
Mana
Interaction Suite
Broken Card Advantage
Next, I'm playing most of the tutor and Cloudstone package, ported from Rograkh's Bouncy House.
Despite the lower creature count than Bouncy House, I'm still playing Earthcraft with enchant lands because it's so powerful with the Cloudstone loops, and this deck also gets Chatterstorm, which goes crazy with Earthcraft.
This is a lot of overlap with Bouncy House, and it allows you to execute a lot of the same strategies, though with fewer backup combos: no Barrin, Master Wizard for Dockside Extortionist, no Kinnan, Bonder Prodigy + Basalt Monolith, and no Devoted Druid + Machine God's Effigy; most of those combos don't come up very much, but they give you a few free wins, so let's look at what we get in exchange and what we have to play to take advantage of Krark, the Thumbless.
Krark Trigger Support Cards
If you have a single Krark trigger when you cast a spell, it's a simple gamble; overall, it's nice because you kind of get a card and mana when you win the flip and you only lose mana when you lose the flip, but the variance is dangerous and the overall effect isn't great. However, if you double the trigger, now you either get to cast your spell three times or you get to cast it and keep it, or, some small portion of the time (25%), you waste your mana (so you still really want cheap spells to mitigate that risk); this position is extremely strong, and the three cards above each create this while offering some additional advantages.
Harmonic Prodigy will double your Eternal Witness, Spellseeker, Trophy Mage, Veyran, and Archmage Emeritus triggers. Veyran will double your Archmage Emeritus triggers (and technically your Harmonic Prodigy prowess), and Roaming Throne will either double your Dockside Extortionist and _____ Goblin triggers if you choose Goblin or your Spellseeker, Trophy Mage, Veyran, and Archmage Emeritus triggers if you choose Wizard.
This is a sparse package, but all your usual creature tutors can find them, and Step Through has been added to increase your access to this effect. If you wanted to go further you could include Sakashima of a Thousand Faces or Spark Double, but I think those cards are much worse since they're expensive and somewhat vulnerable to removal when you cast them, so in the interest of card quality I'm sticking with just the best options.
Krark's Thumb isn't exactly an additional Krark trigger, but when you have two Krark triggers, the Thumb massively increases the chances that you get the outcome you're looking for, which makes your spell combos much more powerful.
A few additional creatures come along to join Krark's supporting cast:
These cards are great with Krark; your goal is to convert casting arbitrary spells repeatedly into generating extra cards and mana, and most spells generate one of those or the other, a few do both, but if you pair Tavern Scoundrel, which makes mana, with a spell that draws cards or Archmage Emeritus, which draws cards with a card that makes mana, you'll typically be able to cast that spell enough times to generate enough resources to win with the mana and cards you've generated when you finally win enough flips that your card goes to the graveyard.
Card Draw Spells
Regrowth doesn't exactly draw a card, but it's the same idea: it increases the number of cards you have when you resolve copies of it. It's fantastic here because your instants and sorceries are so great. Gitaxian Probe (which I frequently call "Krark Naus") is one of the best cards, since you don't need to make mana and you can basically just keep casting it until you win all the flips. Consider is maybe one of the weaker cards in the deck, but it offers a good amount of selection with its card draw for a good price, and instant speed is very nice; you could play Brainstorm instead, but because it's difficult to shuffle between many copies, Consider is generally stronger to copy.
Mana Production Spells
In Rograkh's Bouncy House, Crop Rotation is one of the best cards because it finds Gaea's Cradle quickly and cheaply. Here, Gaea's Cradle isn't as good, and finding it isn't as important, but Crop Rotation is extremely powerful to copy because you don't need to sacrifice additional lands for the copies, so for one mana you could sacrifice a land and put three lands onto the battlefield untapped, and one of them happens to be Gaea's Cradle.
Emerald Charm is best when it's untapping Gaea's Cradle, but sometimes untapping Sol Ring or Mana Vault and a regular land is good enough; this makes highly variable amounts of mana depending on what else you have, but even when it's not at its best as a mana source, it also doubles as enchantment removal, giving the deck a cheap answer to Rule of Law effects or opposing draw engines.
It could be considered ambitious to consider Chatterstorm a mana source: you need to have either Gaea's Cradle or Earthcraft to accomplish that, but it's extremely good when you do. Alternatively, it's just a storm card, which is primarily good for abusing Archmage Emeritus. Note that while I really love the dream of popping off with Chatterstorm, there's a good chance that Storm-Kiln Artist is a better card to play in this slot as a way to make extra mana while playing the rest of your cards.
Cards That Make Mana and Draw Cards
These are some of the best cards to copy because they give you everything you need, and one of the biggest advantages of paring Krark with Thrasios rather than Sakashima is that you get access to Growth Spiral and Manamorphose.
The only thing that's possibly more broken with Krark than these are free cards because with a free spell, you're never really behind. If you lose a flip, you just try again, and eventually you'll get at least two copies of the spell. What you really want is to have multiple Krark triggers and to always lose at least one flip so that you can just keep casting them indefinitely. The reason Krark is so hard to play against is the way it plays with free counterspells: they'll counter your card, and sometimes it won't cost them anything, no cards, no mana, nothing.
If they have Archmage Emeritus, they might just get some cards for free for your trouble, and when they win multiple flips they end up with multiple counters pointed at your spell, so you can't really fight over it. The best counterplay is to counter their counterspell before they flip any coins so that it can't go back to their hand, but even if you do that they can win the flip and still counter the spell you were trying to resolve. We'd be playing the free counterspells regardless of Krark because they're very important in the format, it's just that Krark makes them that much better, but we also play additional free interaction to take advantage of Krark.
Free Interaction
Sometimes Mogg Salvage won't be free, but that's very rare. More often Submerge won't be free, but we can play Yavimaya, Cradle of Growth to help with that. These cards are great interaction because they end up answering lots of opposing cards for free, but where they really shine is when combined with Tavern Scoundrel or Archmage Emeritus.
The final sorcery I'm playing that wasn't in Rograkh's Bouncy House is Grapeshot: this deck can generate some big storm turns, and Grapeshot can clear a board, draw your deck with Archmage Emeritus, or even kill the table in some situations.
So that's the "Krark half" of the deck: seven dedicated support cards to make Krark work and a bunch of instants and sorceries that make mana and draw cards.The cards that make mana and draw cards ultimately help execute the Cloudstone combos, and I think this deck will usually win games with an infinite loop rather than just by copying spells with Krark, but the spells you copy with Krark help reach a position where it's trivial to find the cards for your loop, cast them, and protect them with counterspells after chaining through a series of advantageous spells with with Krark.
Closing Thoughts
It's a weird mashup: a storm deck and a creature combo deck, but in this case, I think the decks are surprisingly harmonious, though some weird opening hands are definitely possible.
As for the lands, they're pretty simple. I've added a basic Mountain and more red fetches because the deck uses a lot more red mana, and I've cut Ancient Tomb, Emergence Zone, and Urza's Saga to account for the greater colored mana requirements. I've also added Cavern of Souls now that many of the most important creatures are Wizards.
Incidentally, as I understand it most popular Krark/Thrasios lists revolve around Song of Creation. That card is difficult to reliably find and even harder to resolve, and I think it asks too much in deckbuilding to make sense given these hurdles. My goal is to make my deck more resilient and harder to play against rather than maximizing my explosive turns with a strategy that ultimately adds too much variance and vulnerability.
And of course, the full decklist is available here and below.