His Own Medicine - Assassin's Creed IV: Black Flag - Freedom Cry DLC

Gave the Gouverneur a taste of his own medicine - 20

This is done in Memory Sequence 9 - de Fayet's Last Stand. You'll make your way to the Governor's Mansion, you need to kill the 4 Heavy Guards standing at the gate with a Blunderbuss shot. This will que Marquis de Fayet to run to the barracks near the shore. You need to then kill the rest of the guards, without killing Marquis.

Now I recommend leading him towards the shore, away from the rest of the bodies. Now you need to Counter him, then Hurt him. This will make him fall over and drop his Branding Iron. Now pick up the Branding Iron and kill him with it.

Branding Iron