I'm starting my full sync leftovers after I beat the game, and I notice one reoccurring thing within the first few missions is "Completed all the constraints in one playthrough". What the hell is that!? Does that mean I have to start a new game to get full sync? I don't want that...
No, it just means get all the constraints in one try per mission. Unlike in the previous games though, you can reload the previous checkpoint if you fail an optional objective instead of starting the whole mission over.
It means you can't do one optional objective and fail the other, then go back and finish the other optional objective. You need to get all of them at the same time.
Which is really annoying, because at first I was planning on doing just one optional objective each mission and then doing the others on my second playthrough to add more replay value.
It seems silly I have to both air assassinate a grenadier AND remain undetected. Those objectives seem to be at odds with each other and make the mission very frustrating, whereas if you had to do one or the other that would make the mission very dynamic in the way you play through it.
To get Full Synchronization on that mission, climb the mast, make your way to the other end of the boat and silently kill the three redcoats (either with your bow or poison darts, either is effective), then when the grenadier is the last one standing, do the air assassination and that will complete the Full Synchronization objective.
You don't even have to kill most of them just on the one side of the boat by the mast. Tehn climb the mast wait till the grenaider is behind the boxes so when you kill him no one sees him die. On the other boat climb the left side and just wait till no ones looking walk in plant the bomb dive off. Even if they see you their detection takes a few seconds to max out so just fast walk to the side dive off and they all go to hell before they detect you. It was frustrating at first then really easy. One of those duhhhh moments I had despite having to retry it over and over for like a half hour. Now I can do it every time.
That's one reason I like the full syncs in this practice practice kind of annoying but reminds me of older nes/snes games. Gaming back then was all trial and error. a 4 hour game lasted months.