+1/+1 counter Commanders, for example Hamza, Guardian of Arashin, use proliferate cards to buff their creatures
Part of a cycle that features the almost-as-broken Gaea's Cradle and somehow the hilariously unbroken Shivan Gorge, Tolarian Academy taps to make a mana for each artifact you control, which led to decks that would dump their entire hand of cheap artifacts, make a ton of mana by tapping and maybe untapping Tolarian Academy, and then use big card-draw spells like Windfall and Stroke of Genius to refill before eventually milling the opponent out with Stroke of Genius, potentially all on Turn 1
It's part Massacre Wurm, part Withengar Unbound, and it's an altogether cool addition to the set, even with clear multiplayer text tacked onto a Standard-legal card
Nostalgia + Innovation: The set pairs classic characters like Ethan, Cynthia, and Giovanni with new mechanics like Trainers Pokmon, appealing to both collectors and players