Guide to Epic Bosses:
Once you have completed all the missions in a Chapter, you are tasked with defeating the Epic Boss. Each fight requires a specific hero to be owned for deployment, which you can see listed after the boss name. So first you need to complete all of the threats on a given chapter, including the final boss, and then deploy the listed hero. Below is a brief summary of the Epic Bosses and the rewards for defeating them, as well as some tips for each one:
Chapter 2:3 - Boss: Elektra, Deploy: Black Cat
Reward - Grecian Sai
Tips: To defeat Elektra, who will be accompanied by two Scrappers, take a strong Bruiser with good HP as Elektra's counter-attack ability can really hurt your team otherwise. Avoid taking any Infiltrators with you as that is her strength.
Chapter 3:5 - Boss: Dr. Doom, Deploy: Spiderman
Reward - The Doombringer
Tips: For beating Dr. Doom, you are actually facing off against three Doombots. You should center all of your attacks on a single Doombot at a time, until it is destroyed - then move onto the next one. This means that you reduce by a third the amount of damage received each turn as soon as one is taken out, whereas if you focus your fire on all three, it will take significantly longer before you start to see results. Also, Doombots can use their own health to heal their allies, so removing one as soon as possible is crucial to stop them from healing each other.
Chapter 4:4 - Boss: Magneto, Deploy: Storm
Reward - Magnetic Field Generator
Tips: Magneto deploys Shields to prevent your attacks from passing through. He absorbs your initial attacks and then defends with either a Positron Shield (positively charged) or an Electron Shield (negatively charged). These shields will protect Magneto from attacks of the same charge type, so the Positron will only allow negatively charged attacks through, for example. Because of this, you should choose your attacks very carefully. Poison and items work well as they are unaffected by it.
Chapter 5:3 - Boss: Loki, Deploy: Wolverine
Reward - Norn Stone
Tips: Loki has the most involved and one of the most difficult boss fights. It consists of three waves, with wave two being particularly tricky as Loki disguises himself so you don't know which one to attack. With this in mind, use area attack items such as Cluster Grenades, Nerve Gas, Kunai Barrage or Molotovs, as these will damage all three of your enemies, regardless of which is in fact Loki.
You can also try having your agent use Support Buffs such as Offensive Accelerator and the Batstone, which boost your attack by 25 percent and reduce enemy defence by 25 percent. This sets you up for Round Two with Loki having massive weakness in his defences, which should make the fight that much easier.
Chapter 6:3 - Boss: Doctor Octopus, Deploy: Black Widow
Reward - Electrostatic Arm
Tips: Doctor Octopus throws a bit of a curveball at you with an ISO virus that infects you. You can send the virus back to him by attacking, however, so you shouldn't find it too tricky to deal with.
Chapter 7:3 - Boss: Green Goblin
Reward - Goblin Glider
Tips: Unusually, you are fighting Green Goblin on his own. You can defeat him relatively easily by employing Bruisers, as the Goblin is defined as a Scrapper class.
Epic Boss Farming of Command Points:
Scoring Critical Hits against Epic Bosses is the best way to 'farm' for Command Points. As they are the hardest fights, you have a higher chance of getting Command Points from your Critical Hits.