4 Reasons You’re Getting an Invalid Deck on MTG Arena

Thopter Mechanic – Illustration by Joshua Raphael

Deck building on MTG Arena is the height of anticipation in preparing for a fun and thrilling battle. However, there could be some hiccups along the way, such as your deck displaying as invalid during the deckbuilding process.

I’ll highlight the reasons why decks are sometimes considered invalid and easy ways to fix the error for each situation. Let's get you to your matches!

What Does the Invalid Deck on MTG Arena Error Mean?

Malfunction | Illustration by Izzy

The “Invalid Deck” error on MTG Arena means that the deck isn’t playable in the format you selected. The error is portrayed as a red triangle with a black exclamation mark inside it. Until the invalid deck receives its proper corrections, this means you can’t play it in that Arena format.

There are a number of reasons that a deck could be flagged as invalid, including not having enough cards to meet the minimum number required or too many cards over the allowable maximum. Perhaps there's a banned card in the build or the cards in the deck aren’t allowed in the format, which can happen if you want to change a deck from one format to another.

For example, if you want to play a Standard deck in Alchemy and your deck has cards from Kamigawa: Neon Dynasty, the deck won't be legal in Alchemy since that Magic set has already rotated out of Alchemy.

Notice that all these errors may also come up when importing a deck to Arena.

Let’s highlight in-depth the reasons why the invalid deck error shows up and the ways you can correct it to get back to playing with your favorite builds.

Not Enough Cards in the Deck

Sometimes you're in the middle of deckbuilding, but then have to save your deck for later and get offline. Your deck in progress comes up as invalid if there aren’t enough cards in the build. Formats like Brawl want you to have the specific 60 (for Standard Brawl) or 100 cards (for Historic Brawl), while Ranked formats usually let you have 60 or more cards without coming up invalid.

If you don’t have enough cards in the deck, open the invalid deck by scrolling all the way to the bottom of your deck collection to find it. Alternatively, you can search the deck’s unique name to bring it up quicker rather than scrolling.

Too Many Cards in the Deck

Most Ranked formats are okay with decks exceeding the minimum number of cards. However, Brawl formats are more stringent in how many cards should be in the build. If you go over the set minimum of cards for Standard Brawl (60 cards) or Historic Brawl (100 cards), then the platform flags the deck as invalid.

You can tell that there are too many cards in the deck because the card counter that comes up as 60/60 or 100/100 cards will be highlighted in red. Most 60-card formats like Explorer and Alchemy allow you to go over the minimum. However, for Brawl formats, you have to remove the extra cards to meet the exact deck size. For example, if the card counter says 106/100, this means you have to remove six cards to make your Brawl deck valid.

A Banned Card is in the Deck

I remember when Core Set 2021 debuted on MTG Arena and I learned about Runed Halo, a reprint from other sets like Shadowmoor and Ultimate Masters. I included this nifty white enchantment in all of my white decks to gain protection from a specific card, primarily the opponent’s commander when I played Brawl or a formidable creature I couldn’t remove from the game. Wizards decided to ban the card from the format around August 2020.

If you have a card in one of your decks that’s ultimately banned in the format you’re playing, you must remove it from the deck for the deck to become valid again.

The Specific Cards Are Not Format Appropriate

Sometimes certain cards eventually become inappropriate for the format over time even if you have built the deck correctly in the past. Especially if you play a lot of Standard Brawl or Standard decks, some cards in your decks may become illegal once the Standard rotation comes.

For example, the sets that will be rotating out of the Standard format in September 2024 are Streets of New Capenna, Innistrad: Crimson Vow, Innistrad: Midnight Hunt, and Kamigawa: Neon Dynasty. If you have Standard decks with cards from any of these sets in them, they’ll eventually come up with the invalid error after the Standard rotation in September.

If cards aren’t format-appropriate, you’ll have to delete them from your deck and sideboard and then edit the build with format-legal cards that do almost the same thing. This is a great option for updating Standard Brawl or Ranked decks when the oldest Standard sets rotate out. Alternatively, you can keep the cards in the build, but change it to a different format to ensure validity, like changing the format from Standard to Historic or Timeless when a Standard set rotates out.

Maybe you want to build a deck around some digital-only mechanics like heist from Alchemy: Outlaws of Thunder Junction – you have to be sure that your deck is for a format that accepts those cards (usually either Alchemy, Historic, or Timeless).

How to Find Valid Decks for Any Format

The Arena Tutor Metagame tab can automatically give you pre-built deck suggestions based on your current collection so you always have a valid deck to play. The deck recommendations are also based on how many types of wildcards you have available to craft your next deck.

Once you get to the Metagame tab, you can browse the suggested decks and pick the one you like best. Sometimes, you won’t have all the recommended cards for the recommended list. Therefore, you’d have to utilize some of your available wildcards to finalize the deck build.

A higher meta percentage means that more players have this deck built on their Arena accounts. Win rates that are 50% or more are the best ones to consider building so you can increase your MTGA ranking as high as possible each season.

Wrap Up

Quick Fixer | Illustration by Francis Tneh

With so many formats and deck building rules for Magic: The Gathering, it can be confusing when deck building as a new MTGA player. If you have a deck with an invalid error, check into it with either one of these four reasons to get to the root of the issue and do less troubleshooting and more playing!

You can check out the Draftsim blog for more deck building resources for Commander and other formats. When you aren’t browsing the blog, you can stay updated by following the Draftsim Facebook page to get notified about new content posted on our website every week!

Happy deck building and remember to have fun in every game no matter what cards you're dealt!