What did Pokémon Gold and Silver add?

Pokémon Gold and Silver, released in Japan on November 21, 1999 and in North America on October 15, 2000, added more to the series than any generation before or since. One hundred new Pokémon took the total to 251, and two new types, Dark and Steel, were introduced to rebalance a game the Psychic type had dominated.

The systems piled up: Pokémon gained genders and could breed at the Day Care on Route 34, leaving eggs that hatch into baby Pokémon. Pokémon could hold items and use them mid-battle. Shiny Pokémon appeared as rare alternate colors. Friendship became a universal stat, roaming Pokémon fled across the map, and Apricorns could be crafted into seven new kinds of Poké Ball.

Above all, the games kept time. A built-in clock tracked the hour and the day of the week, changing which Pokémon appear, when berries regrow and which events run, so the world moved whether or not the player was in it.

And after the Elite Four, the games opened the whole of Kanto, the first region, as a second campaign with eight more badges. Gold and Silver did not just continue the series; they set the checklist every later generation would be measured against.