Note that cracking a fetchland counts as searching their library, so folks might not break that Terramorphic Expanse or their Polluted Mire unless they are needed, which is still a win for you as you slow them down
However, listing cards on these 2 sites is a great way to reach casual players that doesnt mind paying above market value for your cards
If youre building a Limited deck, then you need to have at least 40 cards
For example, you could have four copies of Mickey Mouse, Wayward Sorcerer and four copies of Mickey Mouse, Brave Little Tailor if you really love the Disney mascot
But as Wizards discontinued the more game-breaking cards from future print runs and gradually reduced the strength of new cards, the status of that original, arbitrary group began to acquire a historic weight they became THE Power Nine, embedded in the games earliest, pioneering era