I know it's the deadest of dead spin-off series, but I still miss the Stadium games. Before Battle Frontiers or Maison reskins, what qualified for Battle facilities in Gen I/II was the stadium games.
From giving nicknamed pokémon changes in color hue to differentiate between them, to a PC and item management system that puts Bank to shame, to a Gym Leader Castle that gave the Gym Leaders more competent teams, to the GB Towers that gave you an official way to get a speed-up button on the games, to the crowd-favorite mini game mode that let you use your own pokémon in it, including alternate pokémon otherwise not available, to the Academy that let you know of specific move combos and strategies otherwise unmentioned in-game, to the Cups that made unevolved or otherwise lower-tier pokémon relevant again, to the bafflingly abandoned ability to do 12 vs 12, 4 player battles from Gen I, to the remixed out of context music (whomever thought making Red's theme a remix of Mt. Moon was insane and I love them
https://www.youtube.com/watch?v=DytrZWAfapo ), I miss the Stadium games.