Assassin’s Creed Chronicles: Trilogy Pack (EP)

At first I wanted to boost it at the very end (the final battle), but those kills don’t count towards the count (it turned out that these were some other type of kills altogether). Here's a video on boost.
Hints from the topic on "AS: India":
(Chapter 3, almost the very beginning) Video transcript for those who have problems using the Helix Blade. The blade can only be used in quick kill mode. We throw a smoke blower, approach the first one, press and immediately , with the second one too. The main thing is that one target is captured, if both are “in sight”, then when you press A double kill will occur without the Helix Blade.
Three positive signs that you have used the Helix Blade:
1. The helix scale is decreasing.
2. A transparent halo in the form of a circle after a murder.
3. The disappearing corpse after the murder.