Her easily payable mana cost and 5-color identity has given her a home in Commander, though, with her WUBRG-generating ability nicely fitting into big mana decks such as Jodah, Archmage Eternal
So as long as development tested the Rats in high numbers to make sure it wasn't degenerate, we knew it was safe to break the rule (well, as safe as development can ever be the real world just has so many more playtesters.) Rule #4 Breaking Rules Is A Test For the Future When we do choose to break a rule, R&D tends to keep an eye on the card
It does not have to be a legal card in the format you're playing or a part of your Draft or Sealed pool
If Bill Ferny, Bree Swindler is removed from combat, it remains tapped if it was tapped
If either target of the Level 2 class ability is an illegal target as the ability resolves, the ability won't do anything