Generation III added 135 new Pokémon to the core video games.
These species first appeared in Pokémon Ruby and Sapphire, released for the Game Boy Advance in 2002, and later appeared in Pokémon Emerald. They occupy National Pokédex numbers 252 through 386, beginning with Treecko and ending with Deoxys.
Generation III introduced the Hoenn region and gave the series a noticeably different group of creatures from the first two generations. Most of its new species had no direct evolutionary relationship to earlier Pokémon, with Azurill and Wynaut being notable exceptions connected to older species.
The figure 135 describes new species, not the total number of Pokémon available in the generation. Counting all species in the National Pokédex after Generation III gives 386. The generation also introduced two Mythical Pokémon, Jirachi and Deoxys, whose availability was tied to special events and related film promotions.