The final encounter with the Russian Mafia Boss is a unique challenge. He is heavily armed and surrounded by bodyguards. This fight is less about direct combat with the boss and more about clearing his defenses. You'll need to systematically eliminate his bodyguards, who are often armed with powerful firearms. Use cover effectively and prioritize taking out gun-wielding enemies first. Once his bodyguards are dealt with, the boss himself is vulnerable. He often carries a powerful weapon, so approach with caution. A good strategy is to use a firearm to clear the bodyguards, then switch to a melee weapon or throw your empty gun at the boss to stun him for the final blow. The 'Tony' mask can be effective for quickly dispatching bodyguards in close quarters.
