Arven provided most decks a crucial way to set up, while Electric Generator was the lynchpin of Miraidon decks giving birth to the saying You live or die by the Generators. Being the first set of this generation, the Trainer cards had to be decent
Honorable Mentions Cards like Blood Artist, Grave Pact, or Zulaport Cutthroat are the backbone of sacrifice decks or aristocrats decks because these decks make creatures die, and you want to profit from that
Its Metallic Turbo attack is unlike any other card and lets you stack your benched Pokemon up with energy, dealing damage and providing support
Towns are a new land type that certain cards will care about
I also think it fun to observe the "evolution" of Kagemaru Himeno's style over the years
Players often remember the moment when Rayquaza descends from the sky to quell the raging battle between the legendary titans Kyogre and Groudon