So on Arena they put up an event where you can get Rhys the Redeemed after one win. Now this card is clearly not standard legal or anything, but you can definitely use it in the brawl decks.
I also, using a wild card sense I really only care about brawl, got a Karn Scorn of urza but I can't use this card in the brawl decks. I check and it isn't ban.
What happens when you try? From what I can tell, they have the deckbuilder set up to only allow for cards that are legal in the deck (they are in Standard, in your commander's color identity, or is Rhys) and I can add Karn just fine and don't get any errors. Are you only seeing an error when trying to join the Brawl queue or when trying to start a game?
I am not going to pay 10,000 gold to join the event since it isn't worth it, but I can try on Wednesday to see if I have the same problem with Karn. Or, someone else can probably try as well. I am not sure why you would get stopped from playing him.
Well, I guess I can't say exactly what is happening in your situation but I don't seem to have the same problem. Maybe trying building a Historic deck (I know it should show up for Standard but this removes the possibility of some filter causing the issue). What happens if you set the filter to show cards you own and don't own? Does it show up then?
While Karn is legal for all Commanders, what commander are you using? Maybe something is weird with what you are choosing (I am using Alela).
The best I can figure is either there is some weird filter issue or you don't actually own the card even though you think you do. The steps above should point to something (even if it isn't one of these two things).
I also, using a wild card sense I really only care about brawl, got a Karn Scorn of urza but I can't use this card in the brawl decks. I check and it isn't ban.
Why can't I use karn even in the other 59 cards?
I am not going to pay 10,000 gold to join the event since it isn't worth it, but I can try on Wednesday to see if I have the same problem with Karn. Or, someone else can probably try as well. I am not sure why you would get stopped from playing him.
While Karn is legal for all Commanders, what commander are you using? Maybe something is weird with what you are choosing (I am using Alela).
The best I can figure is either there is some weird filter issue or you don't actually own the card even though you think you do. The steps above should point to something (even if it isn't one of these two things).
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That is a simple, and direct, answer to the problem OP is setting.