Think of them as a Stage 3 evolution they are played on top of fully evolved Pokemon, acting as an additional Stage and providing new moves with a stat boost, too
Not only that, but some Dark Magician cards are so powerful, many Decks are playing it that aren't even focused around Dark Magician itself
Cards where the flavor text undermines or contradicts established canon, ridicules the card its on when the original purpose of the cards wasnt to be funny, or basically any flavor text that makes the world more uninteresting or unnecessarily contrived wont make the cut
4 X Speed Helps Make a Quick Change Smart Retreats Can Make a Big Difference Retreating is an important part of the strategy that comes with Pokmon TCG Pocket
In addition to this, a big part of the reason these cards were so popular was because the mana in that Standard format was quite bad, to the extent that you were pretty close to wanting Attune with Aether in your decks even before the energy bonus, but once you have the energy bonus you might as well play Harnessed Lightning, which means you may as well play Rogue Refiner to power up your kill spell, and so on
And thats about where the good stuff ends, because Peters main ability, Youre Next!, is useless unless you are playing against a pirate deck