Some of our friends complaining that they can not defeat Bosses in Vegas city on District 3 and also 5.
And why they can not succeed? Because the Boss has tons of Health!

For example Boss on Disctrict 5 below:

She has 25000 Health points!
I notice that we can have variance of Health for this Boss on the same District.. The one above has 25000 Health, some friends has 15000, and I got 1000 Health... lucky me?
Is it because I only on level 1 mastery now, so only have that much on her health? Anyone please advise?

Ok, no matter how much Health the Boss has, we can still beat them!
How to? Ok, first I got one tip from Pedro telling me to have my full of Health first.. then use a Stun Gun to attack her!
I did but nothing's happening! Guess the tip is not good for me, Pedro.. so I just use Attack button to make her lose some Health points..

My henchmen sacrifice themself for me..
I keep attacking her, using my kits.. I use the Grenade, the Shiv, use Attack button again and heal my self with the Health kit.. but somehow the Boss is able to heal themself as well! She has a full health again! Crap!!!
Then I just click on "Ask for Help" button and publish! I think it works!
I still attacking her but she quickly loose her Health... I guess my best mafias are helping me to defeat her quickly, hooorrraaaayyy!!!

The point is, ask for help is the best way I know to defeat any Boss in fight!
If these tricks do not work for you, you have problem with your game.. please contact Zynga Support team about this..
I hope you can defeat the Bosses to now.. and if you know any other tricks, please kindly share on the comment section below..