Enter the profile name "V Pirate" to unlock all cheats. You can get to the cheats section under the Extras menu.
When you grab enemies with skulls over their heads, you can get information from them. In order to do special kills, you must walk over to a purple skull shining out of the ground with the enemy. To do this, you must grab him and take him over to the purple skull. Then, use his own method.
Defeating The Russian On The Island:
When you get off of the gondola, take a right into the shed. Do not go to the launch pad yet. Get the ammunition for the sniper rifle. Leave the shed and make a right to the steps to the missile launch pad. Walk up the steps and the Russian will say 'We have to stop meeting like this, Big Boy!'. He will stay on the catwalk above, throwing flaming barrels at you. Shooting him is useless. Watch the Russian through your more precise aiming (it is easier this way). When he lifts a barrel, he will walk a little way, lift it above his head, and it will catch fire. Shoot the barrel while it is on fire before he throws it at you. It will explode in his face.
After two or three explosions, guards will begin to appear from the right and left sides of the map. Take them out if they give you a problem, however try to focus on the Russian. After the Russian's life gets half-way down, an intermission sequence featuring him catching ablaze will play. He will then jump down and chase after you. Get him to chase you into the piles of barrels scattered in the corners of the map. There is one barrel in each pile that will light (usually the brightest one). Get the Russian to walk into the barrel and it will ignite. Then, shoot the barrel to blow it up on the Russian. Be careful not to get too close or you will sustain damage. After about four to five explosions, he will be defeated. If the Russian runs into a guard, the guard will also catch fire.