Pokémon Gold and Silver added 100 new Pokémon to the Pokédex.
Released for the Game Boy in Japan in 1999, Gold and Silver introduced the Johto region and expanded the series’ roster from 151 species to 251. The new Pokémon included Chikorita, Cyndaquil, Totodile, Lugia, Ho-Oh, and the baby Pokémon Pichu, Cleffa, and Igglybuff.
The games also introduced several mechanics that became series standards. Pokémon could hold items, eggs could be bred at the Day Care, Pokémon had genders, and the in-game clock supported day-and-night cycles and weekday events. Gold and Silver also added Steel- and Dark-type Pokémon.
The total of 100 can be confused with the original generation’s 151 Pokémon or the 135 added by Ruby and Sapphire. Gold and Silver’s new species were numbered 152 through 251 in the National Pokédex, beginning with Chikorita and ending with Celebi.