This was created to go alongside MGeffro's guide, titled, "Heroic Battles Farming". It's just a basic runthrough of exactly how much energy it would cost you to unlock the heroic battles for every mission. That way you can make some kind of plan to farm E-ISO's, and utilize the most energy you possibly can. MGeffro's guide can be found right here (http://avengersalliance.wikia.com/wiki/User_blog:MGeffro/Heroic_Battles_farming)
To explain a little bit further, if something says 30 energy, I mean it will take three wins of whatever kind necessary for the heroic battle to show up. In S2C2M4, it only takes one win for the heroic to show up, granted that you make up the other point from doing the deploy. You'll understand what I mean if you look at the link above.