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Pokemon Emerald: Double Battles
Just like in Ruby and Sapphire, Pokemon Emerald will have double battles. In Emerald, though, double battles can be fought with two totally different trainers and you, or two of the same type of trainers and you like in RS. Below you can see how two trainers can spot you at the same time, and both will enter a double battle against you.

Talking to Sailor and spotted by Tube Girl

Talking to Tube Girl

Entering the double battle against Sailor and Tube Girl