This feature will only be available in the future. Just like the other Players around you, there are Super Powerful Bosses owning different parts of the Mafia World. These bosses should be dethroned in your way to be the greatest Mafioso of all time. The bosses may require multiple beatings to conquer them and their city. They will not surrender easily. Hence, you should attack them until they surrender and once they surrender they will join your side as you super powerful Mercenary.
The boss fight can be initiated from the Fight button at the left bottom corner and then the Boss Fight button in the Left-hand side.
The bosses will be listed here.
*Big Billy
He was the back-stabbing rat who put you behind the bar. He runs the Neighbouring hoods and it is time to attack and invade his turfs and claim back what was yours.