Other known variants
x2Dual Brains
During your turn, you may play 2 Supporter cards.
Gyro BallSwitch this Pokémon with 1 of your Benched Pokémon. Then, your opponent switches the Defending Pokémon with 1 of his or her Benched Pokémon.
If I have two Magnezones in play with the "Dual Brains" Ability, does that mean I can play 4 Supporters during my turn?
No, you cannot. Dual Brains says you may play 2 Supporters, period; it doesn't say "an extra supporter" for each Magnezone.
What happens if I use Bronzong's "Gyro Ball" attack but I don't have any benched Pokemon?
You have to switch Bronzong if you are able to; the "if you do" part refers to when you have no Benched Pokemon. So if Bronzong doesn't switch the opponent's Active Pokemon doesn't switch either.
The version of "Gyro Ball" attack on Forretress says "you may switch..." as an optional action, but the version of "Gyro Ball" on Ferrothorn indicates the switching part of the attack is mandatory. Which way is correct?
The effect may vary from card to card, so you should play each attack as it is written on its card. So for Forretress the switch is optional, but for Ferrothorn it is mandatory.