You are playing as the CIS against the Gungan Grand Army. All the units are the same except the Super Battle Droid is replaced by the earlier Battle Droid. The Gungans have the shield generator like in the movie, but it really doesn't have an effect on the battle other than blocking incoming attacks. The Gungans are heavily armed with their plasma grenades which act like the Republic's EMP Grenade. Best tactic is to use an AAT that is standing idle outside the shield in the attempt to bring the shield down. Get on the AAT, drive it inside the shield, and continue to fire on the shield generator until it got destroyed and the shield lifts up. Note that the EMP grenades are very dangerous against the tank and will easily destroy the tank. It is wise to jump out of the AAT when the health is low and find a new tank.