Which Pokémon game introduced breeding as a major gameplay feature?

Pokémon Gold and Silver introduced breeding as a major gameplay feature.

Released for the Game Boy Color in Japan in 1999, the Generation II games added Pokémon Eggs and the Day Care system. By leaving compatible Pokémon at the Day Care, players could eventually receive an Egg containing a newly hatched Pokémon.

Breeding expanded team building beyond catching wild creatures. It allowed players to obtain baby Pokémon, pass down selected moves, and work toward particular abilities or statistics in later games. The feature also connected naturally with the series’ themes of growth and evolution.

Breeding should not be confused with evolution. Evolution changes one Pokémon into another species, while breeding produces a new Pokémon from compatible parents. Gold and Silver also introduced Pokémon Eggs through the story and added the baby Pokémon Togepi and Pichu to the series.