>>44217371it was introduced in the ex era since Gen 3 introduced Doubles and they wanted to hype off that in the TCG but it was promptly forgotten about like a couple years into the ex era and completely retired in the DPPTHGSS era. it's why if you read any card from the ex era they HAVE to say "defending Pokemon" instead of "active Pokemon" due to the fact that someone COULD be playing the Doubles format.
you can read some old-ass rulings about it here.
https://compendium.pokegym.net/compendium-ex.html#two_on_two_gameplay 