Which Pokémon battle feature was introduced in Pokémon Ruby and Sapphire?

Pokémon Ruby and Sapphire introduced double battles, in which two Pokémon fight for each side at the same time.

The feature changed the series’ traditional one-on-one battle format. Moves could target one opponent, an ally, multiple Pokémon, or the entire field, making positioning and move selection more complex than in earlier games.

Ruby and Sapphire were released for the Game Boy Advance, first in Japan in late 2002 and internationally in 2003. They also introduced Pokémon Abilities, Pokémon Contests, the Hoenn region, and 135 new Pokémon. The games were directed by Junichi Masuda and developed by Game Freak and Nintendo.

Double battles later became a regular part of the competitive and story modes. They should not be confused with multi battles, which also appeared in the same generation but involve two Trainers on each side, with each Trainer controlling one Pokémon.