Here's how I killed that guy, unconventionally:
As the fight starts I keep looking for queer ways to take him down, starting with basic swordfight tactics, which becomes a failure as he knows how to counter all my moves. Then come smoke bombs, but he could unfailingly see through all the smoke and so he remains unbeatable. And then I shoot darts with all the possible properties upgraded to their highest potential through my blowpipe, yet he turns out immune to their effects. (And as I knew his bullets wouldn't bounce off me, I had put on the Mayan outfit for additional protection.) After that I try to gain higher grounds and once succeeded, throw rope darts at him to strangle him, but possibly because he has a thicker neck or heavier body due to all that armour he has wrapped himself up with, the ropes would break off and he would be released over and again. But he never pursues me to the top and remains down below. Then I climb up to a wooden beam from which I could jump down and air assassinate him but I have something else in mind and the idea of doing so or even attempting it remains unthought of possibly because I presumed that the guy has hightened senses and so he would be able to block my attack. Therefore, I make the move as planned. At first, I throw a smoke bomb at him, which although fails to daze him, could have possibly held him inside the field of effect while I make my finishing moves. I do jump down upon him, not to instantly assassinate, but to tackle him so he falls on the ground and lies there, helplessly, with his behind turned towards me. Finally, I finish him off with a brutal sword slash through his armoured back.