The second generation added 100 new Pokémon species to the original Pokédex total.
Pokémon Gold and Silver introduced the Johto region and expanded the collection from 151 species to 251. The new species ranged from Chikorita to Celebi in National Pokédex order.
Generation II also added major mechanics, including a day-and-night system, Pokémon breeding, held items, and the Dark and Steel types. Players could travel to Kanto after completing much of the Johto adventure, linking the new games to the original region.
The figure is sometimes confused with the 135 species introduced by Generation III. It is also distinct from the final Pokédex available in Gold and Silver, which includes the original species as well as the 100 new additions.