Virtual-On Force

This boss battle is a bit trickier than the last if you aren't quite sure about what you're doing. First and foremost, these mechs won't take much damage if you try shooting them from the start. That said, you should primarily focus on trying to evade their attacks. I found that jumping up with Y and tapping A to drop back down helped evade many of their attacks. After a short time, they'll form together in the shape of a giant crystal and this is when you're supposed to really lay in to them. If you've got a decent mech with any EX bonuses you should be able to take them out with one transformation.

Personally, I'd suggest doing arcade mode after you've done some missions and have upgraded your AI, otherwise the bosses will make quick work of your partner which puts you at a severe disadvantage. If you've picked up any gems make sure to use the EX points by pressing Y at the Arcade Screen and put them in to either health or damage. These help tremendously when playing the game.