What new battle format did Pokémon Ruby and Sapphire introduce?

Pokémon Ruby and Sapphire introduced double battles.

In a double battle, each side uses two Pokémon at the same time. This changed how trainers selected moves because attacks could target one opponent, affect allies, or strike multiple Pokémon depending on the move.

The games also introduced abilities and natures, which added further strategic variety. Abilities give individual Pokémon special effects, while natures influence statistics and sometimes determine which stat grows more strongly.

Multi battles were added alongside double battles, but they are not identical. In a multi battle, two trainers share a side and each controls one Pokémon, whereas standard double battles generally involve one trainer controlling two Pokémon.