- Stay out of combat
- Use two guards as a human shield
Fast travel to Havana and quietly make your way to the assassin to start this memory. Although you don't need to stay out of combat, it is a good idea to anyways to avoid wasted time. Start by making your way across the roofs, Sleep Darting the Gunner, and then knock out the Gunner and follow the roofs along the wall of the main area to finally spot El Tiburon.
Backtrack the way you came and when the men turn east just stay on the roofs and follow them quietly. When they stop to kill a few men in the open wait for them to pass and then head to the building across the way so that you are now on the right side of the men and continue to follow them over the roofs. Kill the first Gunner you come across and then Sleep Dart his friend to the northeast and kill him as well. Continue north and Sleep Dart a Scout on the roof and a Gunner just a little further ahead and El Tiburon will enter the fort.
The objective to stay out of combat will officially begin and you should take it slowly and carefully from here on out. Free run through the trees to the outer wall and climb up, being careful that the Gunner is facing away when you pull up and assassinate him. Sleep Dart the Scout on the south side of the fort before you take him out and then do the same for the one to the north of where you jumped into the fort. You can now go out onto the rope above the courtyard and air assassinate Torres.
In the fight with El Tiburon that follows, you will want to focus on the optional objective of using the plain soldiers and human shields against Tiburon's pistol. Once you have the objective filled, you can go to work defeating El Tiburon. If for any reason you run out of bullets and the game bugs (as it did for me) so that you can't open the chests for more ammo, lose El Tiburon and loot some of the bodies for more ammo.
After the scene you will need to escape the area and hide. This can be done easily by jumping into the ocean and swimming south and then make your way to the waypoint.