Monastery Swift-guide

Argus is playing against Neferian in round 3 of a Modern PPTQ. Neferian mulligans, keeps his 6 card hand and scrys to the top. Argus starts the first turn of the game, plays a Mountain, casts Monastery Swiftspear and attacks. Neferian flips the top card his deck thinking Argus has played a Goblin Guide. Argus immediately calls a judge and explains what happened. What do you do?

Judges feel free to answer on Judge Apps!

Neferian receives a Warning for Looking at Extra Cards, since they took an action that enabled them to see the faces of cards in a deck that they were not entitled to see. This infraction is not Hidden Card Error because it is correctable with publicly available information.

The fix is to shuffle any seen cards, if they were previously unknown, into the random portion of the library. Since Nefarian previously knew the identity of the card that was mistakenly revealed, we leave the card where it is and we do not need to randomize the remainder of the library.