The first target in Assassin's Creed IV, Julien du Casse is the captain of a Spanish Galleon in port at Great Inagua. For full sync you need to stay out of combat and finish du Casse with an Air Assassination. I chose to do an Eagle Etrike, which can fulfill both requirements.
The controls have been further simplified for AC4. Basically all sprinting, free running and climbing can be done with two buttons: + . Even the climb leap maneuver at the beginning of this video is automatic. The only time you need to add is to force an unsafe jump (such as to initiate an Eagle Strike).
The range of Air Assassinations has been extended to nearly equal the height of a fatal fall. This makes Stunt Assassinations quaint because in most cases you'll be passing up an opportunity for an air in order to do a similar aerial assassination that doesn't work quite as well.
Getting back to the controls, an Eagle Strike begins with + + as usual. Catch Ledge has been simplified. You no longer hold . Instead, you just aim Edward's hands using left . In this video I held it . Air Assassinate has also been "simplified" in a way: no more target locking . Now you just look at someone and press . This can actually make some assassinations more difficult if your target is in a group or behind you. For this video I used right during the fall to aim the camera at du Casse.