Killing blow

Note that this is not limited to fatalities or similar in fighting games. The killing blow can be the first and only strike delivered. Commonly the NPCs are capable of the same thing. If it requires the opponent to be reduced to 20% health or something before using, then this does not count (this is NOT for impressive final strikes).

If all characters have only 1 hit point to begin with, something else might be more appropriate than this tag.

Commonly boss and elite characters are either immune to this or have extraordinary ability in avoiding it. Other limitations in use may exist, such as not working against vehicles.

If this requires an unique condition to be met to perform which can't be trivially repeated, then you might consider something else (e.g. backstabbing generally requires the target is completely unaware of your existence).

Instances where the ability to do this is limited to a small section of the game, only achieved later on as an ultimate death dealing skill, a small statistical critical hit chance, with a damage/instakill power-up, or such should not count. This effectively negates many RPGs and especially games marked with obsoleted assets.

Common in: tactical shooters, stealth games, ...
Unlikely to ever appear in: RPGs, fighting games, ...