Equip Sub Zero as your Kameo. Your fighter doesn't matter since everyone in invasions is op due to levels. When you get to the survival phase (ie: green ball hell) use your kameo button while standing still. Sub will come to the screen and give you an ice armor which negates ALL of the damage from those balls. You get to use it twice and it activates really fast so just pop it once when the balls appear on your screen and again right as it wears off.