What major battle feature did Pokémon Ruby and Sapphire introduce?

Pokémon Ruby and Sapphire introduced double battles as a major battle feature.

In a double battle, each side uses two Pokémon at the same time. This changed the series’ traditional one-on-one format by making positioning, move targets, and teamwork important parts of battle strategy. Some moves could affect multiple combatants, creating possibilities that did not exist in ordinary single battles.

Ruby and Sapphire also introduced innate abilities and natures. Abilities gave Pokémon special effects, such as immunity to certain move types or increased power for particular attacks. Natures influenced a Pokémon’s statistics, adding another layer of variation between members of the same species.

The games were released for the Game Boy Advance and took place in the Hoenn region. They could not directly link with the previous generation’s Game Boy games because the older and newer link-cable systems used different technical specifications.