Latest guide on how I beat Villain Siege all 9 bosses:
Boss 1 to 3 - use She Hulk, Sister Grimm, or Singularity (they are my 3 weakest heroes) to try beat 3 of them. If not strong enough use 4* Blade, Blackcat, or Ironfist to finish it off. Usually first 3 boss is very easy.. except Dr Oc have to careful lasers.
Boss 4 to 5- use 2 heroes, 4* Blade, Blackcat, Throot, or Ironfist combo.. if not enough throw in Nebula 4* also.
Boss 6 - need 3 heroes. These days often use 4* Elektra (leader for speed mastery), 5* Kingpin and 4* Bullseye (both with suit) combo. For sure will beat this boss easily thanks to 'free' 5* Kingpin.
Secret Wars Bosses 7-9 (the real tests begins)
this is where things get REAL HARD. Depending on what position the bosses are I will utilize the type of heroes to handle them.

Boss 7 (from here onwards team bonuses, and mastery is very important)
- if Kingpin is first - use Sharon Carter 5*(leader for cooldown mastery), Black Widow 5*, Mockingbird 4* . They 3 can reduce his HP to almost half. Then try finish off with Ronan 4* (leader for universal class def,att mastery), Blackbolt 5*, Cap marvel 5*. If still left some HP use Hawkeye 5* solo to finish him off, or add another hero like Yondu 4*
- if Venom or Maestro is first - use Modok 5* (leader for energy dmg+ mastery), Red Skull 5*, and Ghostrider 4*. They'll reduce his HP to almost half.. then switch to Ronan 4* (leader for universal class def,att mastery), Blackbolt 5*, Cap marvel 5*. If still left some HP use Black Panther 5* solo to finish him off, or add another hero like Hawkeye 5*/Yondu 4*
Boss 8
- if Kingpin is here, - use Sharon Carter 5*(leader for cooldown mastery), Black Widow 5*, Mockingbird 4* . Won't be as effective compare to if he's Boss7, so just do what damage that you can here. Next bring up Cap America, Falcon, Wintersoldier all 5*s and try bring down his HP even more. Finish off with Spiderman 6*, Daredevil and Punisher 4* (by this time it's overkill already).
- if Venom or Maestro is here, this is where u need physical damage reduction / shield. 2 heroes as leader rocks here which is Angela and Luke Cage. Angela 5* (physical dmg reduce alot with her mastery) I will partner her with Rocket Racoon 5* and Wasp 5*.. rocket lay mines and lure him , wasp keep making him miss, and angela as backup. Luke Cage 5* (his shield triggers and blocks all physical damage, keep rotate when the shield is gone) I will pair him with Maestro 6* and Red Hulk 5*, by then venom/maestro boss should be dead. Another good team to keep vs Venom is Malekith, Thor & Loki 5* - reason being Malekith as leader can change those stuns/snares by Venom to a positive shield buff+.
Boss 9
- Hardest boss to beat. Make sure u keep as many 6*s here as you can. The team I find useful for any 3 of those boss variants are Ironman 6*(as leader for cooldown), Iron Patriot 6*, and Hulbuster 5*. Since this team is so damn strong keep them for later when the boss drops down to 50% or close HP before using this Iron Mania team. (Why? Because the boss/lasers will be more aggressive once the villain boss HP is low... so u need a stronger team near the end of it!)
Use any combos remaining e.g. Venom 6*, Goblin 5*, Dr Oc 4* combo, or Ultron, Vision, Destroyer 5* combo, Goliath 6*, YJ 6*, Antman 5* combo (<--- this is also an OP team once u get their ISO and gear levels up), or GoTG Starlord, Gamora, Drax 5*.. any remaining team just dump here and fight him till 50% hp then throw out your Iron Mania team and watch them turn whoever boss it is to shreds.
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Enjoy! This is how I beat all 9 bosses of Villain Siege everyday.. by the time I finish these days still will have around 6 -9 heroes left. Hope it works out for you too.

If you still struggle even when your teams are close to the above, just upgrade their gears and ISOs more (good ISO sets matter). All the best!
This post has been edited by Davidtcf: Sep 24 2015, 01:41 AM