First, Phantom Dharak is 670, not 640. So I'm at 790.
I activate the ability card, Rain of Shadows. Since I am on your gate and have an Aquos Bakugan, you get no gate bonus.
Next, I activate Phantom Dharak's special ability. (Not a card, I think this is how I do this.) Phantom Dharak gains another 80gs from his Double-Stand.
Me: 790+80=870
You: 880-120=740