The gold and red buttons on the Power Activator have different uses based on what mode you're in.
Press the gold button to scroll through different enemies. A second recruit can then use the Activator's red blast button to play as that enemy.
If you're using a Smart Figure, make them an ally or enemy using the gold button.
J.A.R.V.I.S. will ask you to complete certain actions by pressing the gold button on the Power Activator.