Perfectionist 50 
Complete 100% of all main mission constraints.
This is a full guide for the 'Perfectionist' achievement. The guide will layout all the objectives you'll need to complete to earn 100% in each Sequence.
The Sequences will be shown in order and will have small details to help you pass each mission as well as videos for added help. If you have any better routes or ways of completing certain objectives, please post here.
Also, any other discussions about this achievement and anything relating to it, should be posted and ask here to save on forum clutter.
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Useful Links
Achievement Guide & Roadmap
Alternative 100% Sync Guide
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Credit
Tyger
GamesSeriesNetwork
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Key (Linked)
Sequence 1 (#2)
Sequence 2 (#3)
Sequence 3 (#4)
Sequence 4 (#5)
Sequence 5 (#6)
Sequence 6 (#7)
Sequence 7 (#8)
Sequence 8 (#9)
Sequence 9 (#10)
Sequence 10 (#11)
Sequence 11 (#12)
Sequence 12 (#13)
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Notes
First off I'm letting you all know there will be spoilers. If you don't want any of the story ruined while you playthrough, please read carefully or not at all.
Overall this achievement isn't too hard but a couple of missions may cause you a few troubles. Just remember that if you fail one of the objectives at any point, the game now has a 'Restart Checkpoint' option. Using this does not void the achievement, so use it whenever you feel it's needed. I'll only be listing the missions which go towards this achievement.
Also take note that I won't be laying out how to constantly do attacks like certain assassinations, parries, sequential combo's etc. Please learn them via the tutorial in Sequences. It simply saves on typing space.