Hello,
It is rather obvious that you have either to stun your enemies or to have the adrenalin finisher talent in the swordsmanship tree. It is also possible to knock your enemies down and then get a finisher kill. Or do you want to know how many different cutscenes with finisher kills there are?
There are 4 (or 5 one for finishing one mercenary, but this finisher is not different from than the others) for human enemies lying on the ground: Maybe there are just 3, if you consider that only the angle of the camera was changed.
There are 20 for human enemies stunned and standing, but in a few cases just the angle was changed so maybe 16.
There are 10 ways to finish off monsters. And some monsters have no finisher cutscenes like higher harpies, they just die, when they are stunned and hit.
There are 5 ways to finish off 2 human enemies with the adrenalin talent.
There are 8-9 ways to finish off 3 human enemies with the adrenalin talent. I think one of them is just a change in the angle.
There are 8 ways to finish your opponent in a fistfight.
So there are 42-49 ways to finish your enemies off. And 8 ways to finish them off in a fistfight.
There are also some finishers in cutscenes but they are no finisher kill cutscenes.
If you're curious about where I found the information, there is a folder for finisher cutscenes in the Red Kit, just looked at them and counted them.
best regards
Nemo