Pokémon Ruby and Sapphire introduced Abilities for individual Pokémon.
Abilities are special traits that can affect battles or exploration. Examples from the games include Torchic's Blaze, which strengthens Fire-type moves when its HP is low, and Zigzagoon's Pickup, which can let it find items after battles.
Ruby and Sapphire were released for the Game Boy Advance in Japan in 2002 and internationally in 2003. They began Generation III and introduced the Hoenn region, 135 new species, Pokémon Contests, double battles, and the Pokémon storage feature known as the PC.
Abilities are different from Natures, which were also introduced in Generation III but affect stat growth and flavor preferences. Mega Evolution came much later, in Pokémon X and Y.