There are so many criteria that a best card must pass through, and everyone has their own rubric for calling a card great
With Bygone Bishop, this isnt a problem, since its a good creature on its own and incentivizes you to play more creatures with low mana value
Her true value comes from her ability, however, which relies on you having other Knight cards in play
It featured in some of the earliest decks in the game, it was a pivotal piece of the Sligh deck which essentially acted as the foundation of the mono red aggro archetype, and its presence has been significant in Modern from the first day of the format as it has featured in many of the formats best decks from Zoo to Splinter Twin to Jund
The kingdom of Alexandria, ruled by Queen Brahne, begins their invasion of other nations under orders of Kuja, the "angel of death" from Terra
This is often used as a way to keep old cards up to date with current terminology, but can also be sparingly used for the sake of balancing the game