Assassin Creed Unity Assassinations: Sivert, le Roi des Thunes, Lafreniere, Rouille, Marie Levesque, le Peletier, la Touche.
Originally I had performed an accidental non-story assassination.
https://www.youtube.com/watch?v=aMGJdSF4oEs#t=253
After further investigation it was found that kills from crouching right behind low objects don't trigger the memory scene of targets. There are two ways to do this: Low profile, which is pulling them over the object and stabbing while they are still on the ground; and high profile, which is jumping out from behind the cover and air assassinating them.
When the game developers changed the situation of memory scenes starting to only hidden blade kills (the only lethal way to kill targets) the "crouching right behind cover kills" got left out.
Sivert
A "crouching cover kill" is possible behind the lift in both low and high profile. For the low profile one you have to lure the target to get close.
le Roi des Thunes
When fighting him, use staggering strike to get the target to a corner and parry his attacks. Sometimes he'll fall off the solitary platform. From (under)ground level there are tables and other low objects to non-story assassinate him from.
Lafreniere
A good place for a non-story kill is the very platform the target stands on during the mission. Use disguise to get there without being seen. Next use cherry bombs for luring. You want Lafreniere to be the one directly in front of you as that's who gets automatically targeted for the kill.
Rouille
Sneak up to the area with Rouille and take cover. Phantom blade bolts are good for stealth kills. While he's inspecting the dead bodies take advantage of the nearby low covers to perform the kill.
Marie Levesque
In the party room, Marie eventually walks past a table, in range for the high profile "low cover kill". Wait while blended in a group until she's close enough.
le Peletier
After performing the optional poisoned wine cutscene, wait while in cover behind the counter. Le Peletier walks that way due to the scripting.
la Touche
I couldn't find a way to get la Touche with a "low cover air kill" while he was on the execution stage, so I opted to make him flee instead. There are two different places he can run to, depending on where you are when the target starts running. To trick the AI, I got detected on one side of the stage to make him flee to the other.
Outside the building a guard appears after la Touche runs, and the one inside respawns. Because of this, smoke bombs help with avoiding combat. The target's waypoint just so happens to be next to a table.