[Scripting Question] How do you make the Synchronize ability copy the opponent's stat stage gains and inflict your losses?

[SuperSpyroDragon64]

Say your opponent uses Swords Dance, raising his attack by 2 stages, and this triggers your Gardevoir's ability Synchronize, which raises Gardevoir's Attack by 2 stages. Your Gardevoir uses Future Sight.

Then you switch out your Gardevoir for another Gardevoir, whose ability Synchronize activates when she's sent out, copying the foe's +2 Attack from Swords Dance. Your opponent uses Leer, reducing Gardevoir's defense. Synchronize activates and your opponent's defense is also reduced as if he was hit with Leer.

Synchronize is a fairly useless and situational ability, but I am confident that these changes would make Synchronize a great ability. How do I implement this change into the game?