in the majority of TCGs, these are known as Secret Rare cards, due to their numbering
It feels very similar to a scrapped mechanic from Bloomburrow that batched together all animal creature types, albeit getting around the arguments of what is and isnt an animal by just listing a ton of them individually
Given the lack of any new black-bordered cards with this mechanic in the last 16 years, mechanic certainly isnt evergreen and probably won't see consistent printing again
When it enters the battlefield, each creature gets -X/-X until the end of the turn
In other games, however, a resolved Mystic Remora just wins the game as players cast noncreature spells with reckless abandon and the cards drawn by this one-mana enchantment eclipse the tables combined efforts
Return it to the battlefield under its owner's control tapped and attacking at the beginning of that player's next declare attackers step