Gatherer erroneously considers Arena commons to be in scope for Pauper legality

[scarletcs]

Quick backstory: in late 2021, Arena added a conjure-only print of Swords to Plowshares. This appeared as a common print at the time (like a token) and it was entered into Gatherer as such. This caused Gatherer to report for nearly a year that Swords to Plowshares was pauper legal. We recorded this as issue #108.

This appeared to be an error, and would be confirmed as such in July 2022 when the Pauper format definition was updated to specifically exclude Arena prints from Pauper's scope of legality. That means today that a card appearing at common in a paper print or in MTGO can render it legal in the Pauper format, but a card appearing at common in Arena cannot make it pauper legal.

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Today's bug: Cards that appear at common rarity exclusively in Arena are incorrectly reported by Gatherer to be legal in Pauper. This affects at least these 24 cards which appeared at common in Arena-only remaster sets or alchemy sets.

For example, Essence Flux has two uncommon paper prints, and one common print in the Arena-only set Shadows over Innistrad Remastered. By format definition this is not Pauper legal, but Gatherer incorrectly reports it as legal in Pauper.

Screenshots for Essence Flux

Meanwhile, the cards Demogorgon's Clutches, Iron Golem, and You Find Some Prisoners were printed at uncommon rarity in Adventures in the Forgotten Realms in paper. They subsequently appeared in the Arena-only set Alchemy Horizons: Baldur's Gate at common rarity. By format definition these cards are not Pauper legal, but Gatherer incorrectly reports them as legal in Pauper as well.

Screenshots for those three Alchemy Horizons: Baldur's Gate cards