Over already? One hit, and three-thirds of your HP are gone! Any time people gather with the goal of hitting each other until one of them keels over, the ultimate trump card would be a weapon, spell, technique, trick, or what-have-you that makes people fall over immediately , without all that annoying strategizing and healing and stuff. The One-Hit Kill is that trump card. Often, the One-Hit Kill isn't humble enough to just kill, instead petrifying , permanently polymorphing , or banishing its victim to the Phantom Zone.
At times, it's not even content with a single target, becoming a One-Hit Polykill. Usually, the One-Hit Kill comes at a price. Sometimes it's a Dangerous Forbidden Technique which to use requires Casting From Hit Points or life span , other times it's just really hard to pull off , or leaves you wide open for a counterattack.
It can also result from a Critical Hit. In video RPG s, it's frequently a Useless Useful Spell because of low hit rates , inability to affect bosses , a prohibitive cost required to cast it, or not rewarding the player for defeating enemies with it such as not giving any Experience Points or item drops , if not all of the above at once..
Tabletop RPGs , by contrast, have a history of letting those pesky spellcasters make these spells insufficiently useless, turning many fights into a mere Quick Draw contest. In martial arts, it frequently takes the form of the Touch of Death. If it only works at the start of a fight, it's a BackStab. If it only works at the end of a fight, it's a Finishing Move. If every enemy attack is a one-hit kill, the protagonist is a One-Hit-Point Wonder. If every attack by both you and the enemy is a one-hit kill, you get Rocket-Tag Gameplay.
There's also a non-lethal variant of this: The One-Hit Knockout. One-Hit KOs usually don't involve anything like forbidden techniques or rare technology, just an immense amount of force applied at once, usually in the form of a punch to the face. Bonus points if a particularly fleshy or swift and satisfying sound effect accompanies the blow. The drawback of this is somewhat self-explanatory: It's not a kill, only a knockout. Still, it gives the user at least a solid five-minute head-start, perhaps even longer, to make an escape or thwart some evil plans before the target can recover and figure out what hit him.
