They either give you agency over how or when they benefit other players, or theyll make sure you get more of a benefit than other players
Spend this mana only to cast a Sliver spell
Preventing lands from untapping can hobble opponents and drawing cards with the other abilities gives you something to do with the time that tap ability buys
A box to hold everything, with 4 dividers to keep it organized
Having said that, if you're not planning on competing in tournaments and you just want to have fun building a deck, there's nothing wrong with simply choosing your favorite Pokmon from the cards you already have
This standard index deck features a simple, timeless back design perfect for poker nights, family games, classrooms, and parties