Assassin's Creed 4: Black Flag Walkthrough Part 62 – Sequence 10 “Murder and Mayhem”

Optional Objectives:
Stay out of combat while finding Hornigold
Air assassinate Hornigold

Once you start the mission, head over to the East then turn to the North once you are past the island. For now you need to stay out of combat if you want to get full synchronization. This means lots of weaving and ducking between ships. Slip between the first few to make it over to the island. From there, keep the island on one side and the rocks on the other. Just after Ade mentions the Devil's Backbone, watch for a patrolling shi[ and a rock to hide behind. Wait behind the rock for no more than 5 seconds then take off again. All you have to do here is make it through to where a Schooner is called out. That is the ship you are looking for. Sink it to start the next part of the memory where oyu need to Air Assassinate Hornigold.

Leave the Jackdaw and head for the beach to the South of your location. Now there are no penalties for starting fights. Just make sure that they are nowhere close to Hornigold. If you get caught in a fight close to him, it removes your chance to kill him with an air assassination.

Head across the island that you land on. On the far side you will want to deal with whoever gets in your way as you go for the South side. Once on the Southern side of the island, make your way up to the heights of it. Deal with the 2 Gunners there and then head to the West. Cross over using the branches to reach the elevated area that Hronigold is in.

On this second part of the island, head to the south and transverse along the edge. This will ensure you do not get detected and help move things along quickly. There is one patrolling Soldier for you to worry about. Either just slip by him as you move West or take up a corner position and corner assassinate him. After that head for the Tower. Climb up to the top of the tower. If you want, Synchronize with the View Point. After that, just perform an aerial assassination on Hornigold to finish out the memory.