Generation III introduced 135 new Pokémon species.
The new species debuted in Pokémon Ruby and Sapphire for the Game Boy Advance, which launched the Hoenn region. They were later joined by the enhanced game Pokémon Emerald and the remakes Pokémon FireRed and LeafGreen.
The first Generation III species in National Pokédex order is Treecko at number 252, while the final one is Deoxys at number 386. Adding 135 new species to the 251 available after Generation II produced a total of 386 Pokémon.
Generation III also introduced abilities, natures, double battles, Pokémon Contests, Secret Bases, and a more prominent system of dual types. Some players remember the generation for temporarily limiting transfers from earlier games, but that restriction does not change the number of new species introduced.