At the time, there was only one format, which was the equivalent to today's Vintage (but at the time was just called "Magic"!)
Here's some examples: Cold Wave Confiscation Cyber Jar Delinquent Duo Dimension Fusion Heavy Storm Painful Choice Premature Burial Snatch Steal The Forceful Sentry Time Seal Lots of Spells on that list, and for good reason
Now, they have legs but there were years when there were no Merfolk being made, so of the four biggest creature types from the first set, they have the fewest numbers because of that
Legendary Creature - Human Assassin Pirate Adrestia Islandwalk (This creature can't be blocked as long as defending player controls an Island.) Whenever Adrestia attacks, if an Assassin crewed it this turn, draw a card
8 Helm of the Host Any card that can help you skirt the Legend rule is worthwhile, but Helm of the Host then takes it further by copying the creature for you
1005 Paradox Pokmon and is part of the M24 EN set, with the card number 011/015