If you build your deck around drawing cards, you may also want to include wheels like Jace's Archivist and win cons like Laboratory Maniac or Thassa's Oracle
Having your largest creature don Argentum Armor means it gains an additional 12(!) attacking damage if you're using Arahbo, Roar of the World's activated ability, and while also providing other bonuses to the creature such as Hammer of Nazahn's valuable indestructible
I think both the Summer Training Tour '99 and the Badge Book are absolutely core/fundamental to the early Pokemon TCG in the US (the tour itself may have been the launch of the TCG in America, period)
On top of that, there are secret cards numbered above 204 with a special Enchanted rarity
Onslaught The card, not the set
This feature not only enhances the gameplay experience but also fosters relationships within the community