Generation II of the Pokémon video games introduced 100 new Pokémon.
The generation began with Pokémon Gold and Silver, released in Japan in 1999, followed by Pokémon Crystal as an enhanced version. These games added the Johto region and expanded the Pokédex from the original 151 species to 251. The new Pokémon included starters such as Chikorita, Cyndaquil, and Totodile, along with popular species including Lugia, Ho-Oh, Espeon, Umbreon, and Tyranitar.
Generation II also connected its new region to Kanto, the setting of Pokémon Red, Green, Blue, and Yellow. After completing the main Johto adventure, players could travel through Kanto and revisit many locations from the earlier games. This large post-game area helped make Gold and Silver feel like a continuation rather than a completely separate adventure.
The number 100 refers to species newly added in that generation, not the total number available in the games. With the original 151 included, the National Pokédex reached 251 Pokémon. Later generations added further species, so the Generation II count should not be confused with the number obtainable in modern releases.