It was likely a printing error, and for the sake of consistency, Wizards has kept that error ever since, and made it a formal part of the card back's design
While these decks can go under control sometimes, these archetypes are surprisingly well balanced against one another

Beyond Booster Contents 3 Uncommonscan be any of the following: 54 Non-foil uncommons 1 Basic land or rare or mythic rare scene cardcan be any of the following: 10 Non-foil full-art basic lands (96.6%) 5 Non-foil borderless scene rares (3.09%) 1 Non-foil borderless scene mythic rare (0.31%) 1 Non-foil rare or mythic rarecan be any of the following: 32 Non-foil rares (82.05%) 14 Non-foil mythic rares (17.95%) 1 Traditional foil card of any raritycan be any of the following: 54 Traditional foil uncommons (83.34%) 26 Traditional foil rares (13.67%) 14 Traditional foil mythic rares (2.99%) 1 Non-foil Booster Fun card or 1 traditional foil Booster Fun card of any raritycan be any of the following: 9 Non-foil showcase memory corridor uncommons (69.44%) 2 Non-foil borderless rares (1.23%) 8 Non-foil borderless mythic rares (2.47%) 14 Non-foil showcase memory corridor rares (8.64%) 5 Non-foil showcase memory corridor mythic rares (1.54%) 9 Traditional foil showcase memory corridor uncommons (13.89%) 2 Traditional foil borderless rares (0.25%) 8 Traditional foil borderless mythic rares (0.49%) 14 Traditional foil showcase memory corridor rares (1.73%) 5 Traditional foil showcase memory corridor mythic rares (0.31%) A traditional foil appears 16.6% of the time

Kain gains flying until end of turn
Theyre world-eating monstrosities in the lore, but theyre also just about as big of a threat as possible
When Bill the Pony enters the battlefield, you get to make two Food tokens, an effect that has tons of potential with token-based decks