From the Workshop: Karn Sees Your Deck, Checks Every Card, and Brews Smarter

Greetings, planeswalkers and researchers! Tamiyo here, with a set of notes I have been looking forward to writing for some time.

Most of the updates I chronicle add something new to the workshop — a page, a panel, a feature you can point at. This one is different. Over the past weeks the work went almost entirely into a single question: what does it actually feel like to build a deck with Karn? Not what he can do in principle, but what happens in the ordinary back-and-forth of brewing — asking for a card, cutting three, changing your mind, asking again.

The answer, I am pleased to report, is that it feels considerably better. Three changes are responsible.

Karn Always Knows What Your Deck Looks Like Right Now

This is the change brewers will notice first, and it is the one I am happiest about.

Open a deck and you get a split view: Karn on one side, your decklist on the other. That deck is your active deck — there is exactly one of them, and it is simply whichever deck you have open. No loading step, no "please read my list," no pasting a decklist into chat and hoping it stuck.

The important part is what happens next. Every single time you ask Karn something, he reads the current state of that deck first. Not the version from the start of the conversation — the version sitting in the panel beside you, this second. Accept three of his suggestions, cut a land, change your commander, and his very next answer is built on that updated list.

In practice this removes an entire category of frustration. Karn no longer suggests a card you added ten minutes ago. He no longer loses track of your curve after a round of edits. When you say "what else does this deck need?", he is answering about the deck you are actually looking at.

There is a quiet companion improvement here too: card search no longer returns cards your deck already runs. Every result is a genuine candidate — something the deck does not have yet — rather than a list you have to mentally filter yourself.

Switching decks is just as simple. Open a different one, and that becomes the active deck. Karn follows you.

Every Card Is Checked Before It Reaches You

The second change is a set of guardrails, and it addresses something that had quietly bothered me for a while: an AI assistant that suggests an illegal card is not merely unhelpful, it costs you the time it takes to discover the mistake yourself.

Karn now validates cards at two points — when he searches for them, and again when he proposes adding them to your deck. Nothing reaches your accept-or-decline prompt without passing:

• Color identity. In Commander, a card's identity must fit inside your commander's. Karn now has your deck's exact colors stated plainly in front of him, so off-color cards are filtered out of search results and refused at the point of addition — including in prose. He will not casually name a green card for your Dimir deck in a sentence he thinks nobody is checking.
• Format legality and ban lists. Cards banned in your deck's format are rejected outright. Pauper Commander gets its own handling: rarity restrictions for commanders and mainboard cards, plus its separate multiplayer ban list.
• Copy limits. Singleton is enforced in Commander, four-of in constructed formats — with the genuine exceptions honored properly. Relentless Rats and its kin can still stack to any number, Seven Dwarves still caps at seven, and basic lands remain unlimited. Karn also no longer implies that these limits are negotiable when they are not.
• Commander validity. Whether your chosen commander can legally lead the deck at all, and whether a partner pairing is a legal one.
• Deck size. Growing a finished 100-card Commander deck past 100 is now caught rather than cheerfully performed.
• Your collection. If you have attached a collection as an allowed card pool, that boundary is enforced at the same gate as everything else.

When something fails a check, Karn is told why — and he tells you, rather than silently going quiet or refusing without explanation. A rejected suggestion now comes with a reason and an alternative, which is what you wanted in the first place.

Rulebreaker Is Handled Properly

A note for those following the upcoming Mystery Booster Commander Edition: it introduces Rulebreaker, a keyword on certain commanders that deliberately overrides a deck-construction rule. Karn understands it.

The same care extends to Rulebreaker's stranger forms. Whtz, the Bibliophile removes the maximum deck size, so a Whtz deck may sail well past 100 cards without Karn objecting. Tolabow, Loch Rascal lets your instants and sorceries share one chosen off-color, and Karn will hold to a single one rather than wandering across the spectrum. Grizzlegom, Hurloon Hero opens the deck to lands of any identity.

The exemptions are narrow by design, and Karn now treats them that way — neither over-applying them nor ignoring them.

A Note on Rule Zero

I should be honest about one limitation. Every check above measures your deck against the official rules of its format — and a great many tables do not play strictly by those. Unbanning a card the group misses, permitting proxies, allowing a silver-bordered favorite: these Rule Zero agreements exist only in your playgroup, and Karn has no way to know about them yet.

Two things soften this. First, the gates only apply to Karn — you can always add any card to your deck yourself, by hand, and nothing will stop you. The checks constrain what he proposes, not what you are allowed to build. Second, it is worth writing your table's rulings into the deck's description or its Rules field. Karn reads both before every answer, and with his improved instruction-following they carry real weight — tell him "our group plays with Golos unbanned" or "proxies are fine, ignore price" and he will build accordingly, even though his automatic checks would say otherwise.

Longer term, we would like to hand that control over properly: a way for the brewer to choose which rules are actually enforced on a given deck and which are set aside. Rule Zero is a real part of how Commander is played, and a deck builder that cannot accommodate it is only half a deck builder.

Karn Is Simply Smarter

The third change is the least visible and possibly the most consequential: Karn is now running on a considerably more capable mind.

I will spare you the machinery. What matters is the effect, and the effect is real. Decks come out better constructed — curves that make sense, interaction counts that reflect the format, mana bases proportionate to the colors involved. Synergies are recognized rather than approximated, and the reasoning behind a suggestion holds up when you interrogate it.

Most importantly, he follows your instructions far more rigorously. If you tell him the deck is budget, it stays budget. If your deck description says no infinite combos, no stax pieces, keep it Bracket 2, he holds that line for the whole conversation rather than drifting back toward generic goodstuff by the twentieth message. Idiosyncratic constraints — a tribal theme, a flavor restriction, a pet card that must survive every cut — now survive as constraints rather than dissolving into suggestions.

He is also more forthcoming. Karn is more willing to explain his reasoning, to help you build strategies he might once have hedged around, and to tell you plainly when your list has a problem rather than politely agreeing with everything.

Brew Something

If you have tried building with Karn before and found the experience a little effortful — repeating yourself, correcting illegal suggestions, re-explaining your deck's plan — I would genuinely encourage you to try again. It is a different tool now.

Open one of your decks and start a conversation, or head straight to the chat if you are starting from nothing but a commander and an idea.

As always, my notes are improved by yours. If something feels off, or if Karn does something clever enough to be worth documenting, come tell us on the MTG Agents Discord.

Until next time, may your draws be favorable and your discoveries plentiful.

— Tamiyo, Field Researcher