Assassin's Creed IV: Freedom Cry Walkthrough Part 10 – “de Fayet's Last Stand”

Optional Objectives:
Kill de Fayet with the Branding Iron
Kill 5 guards with the blunderbuss

Head into the Maroon Hideout to begin this mission by talking with Augustin. From there you will be taken to Port-au-Prince that will put in position to make a run to the governor's mansion grounds. Just head straight in to the East to get there. Entering through the front is a bad idea. Instead you want to head over to the Southeastern cover of the area. This will let you slip in through the break in the fence that you used to escape the grounds last time. When Adewale enters the grounds a cutscene will run.

Carefully leave the Stalking Zone you landed in and climb up onto the top of the mansion. Use this time to make sure that your Blunderbuss is loaded. Go to the edge of the overhang at the front of the mansion. Choose firecrackers and through them into the bushes nearby the stairs. This will lure a large number of guards over. Jump over them then pull out the Blunderbuss and fire on them. If you have the portable cannon, there is a great chance you can take out 5+ in a single blast. After that chase down de Fayet. There are a few points when you can just catch up with him and kill him. If you are after just completion then move in and kill him

If you want to complete the memory with full synchronization then wait for him to get to the fort. There, use Smoke bombs to quickly finish off the soldiers, Captains and Jailers. When it is just de Fayet, go unarmed and then disarm him. After that he will pull out his sword. Now just kill him with the Branding Iron to complete the memory in Full Synchronization and the DLC.