As Lethal as It Needs to Be

The Hero is doing his usual thing: battering Mooks left and right with his trusty Phlebotinum Sword and leaving them out cold. Except for that one mook who he clearly just gutted. With the same sword and with the same moves. How?

Because we said so. That's why.

This trope is all about weapons or attacks that seem to jump between lethal and non-lethal as the plot demands. No explanation as to why said weapon's killing power seems to come and go. It simply does.

Compare with Inverse Law of Utility and Lethality and Inverse Law of Sharpness and Accuracy. Contrast with Nerf Arm. See also: Bloodless Carnage, Could Have Been Messy.

For a specific video game version, see Set Swords to Stun.

Anime and Manga

 * The Gatchaman weapons qualify. Sometimes depicted as lethal, sometimes not. The only two that had definite lethal variations were Jun's yo-yos, which could be turned into bombs; and Jinpei's bolos, which could be loaded with timed explosives.
 * Justified in Magical Girl Lyrical Nanoha, most notably in StrikerS. Everyone uses 'magic bullets', which are explicitly stated to be as lethal as they need to be -- that being one of the reasons why Mid-Childa outlawed old-fashioned 'slug-thrower' weapons and became a magic-driven society. Thanks to that, Nanoha is able to repeatedly pull off her signature 'befriend by superior firepower' trick without worrying about accidentally killing someone...
 * In One Piece, it's stated that the best swordsmen can do this: Strike a sheet of paper or a tree branch harmlessly, yet cut rocks or even steel the next second. Zoro reaches this level during in the Alabasta arc.

Comic Books

 * Captain America's shield is like this, Depending On the Author. Sometimes the edges are portrayed as razor sharp, other times blunted.

Live Action TV

 * Xena's chakram is the Trope Codifier. It's usually used as a non-lethal Precision Guided Boomerang, but on occasion, we've seen it cut through rope, wood and human body parts. Callisto managed to throw it hard enough to go through Xena's sheathed sword and into her back.
 * She also once kills Joxer with her chakram by throwing and embedding it in his sternum.

Tabletop Games

 * Dungeons and Dragons usually does this with its abstract combat system, varying the method with each edition. In 4th edition, the final attack is supposed to declare whether it was meant to be lethal or nonlethal.

Video Games

 * Amaterasu's Power Slash ability in Okami can cleanly cut trees, boulders and various minor demons in half, but when performed on friendly NPCs, it will simply knock them back.
 * In Final Fantasy IX, Beatrix's Climhazzard and Stock Break attacks freely switch between doing normal damage and doing exactly enough damage to set HP to One depending purely on the story.

Western Animation

 * Avengers Earths Mightiest Heroes: Wasp's stings are usually portrayed as annoying at best. But during the five-part pilot, she manages to whip off a blast that cut a railroad car in half (a railroad car that was being thrown through the air right at her). It didn't even seem to be a matter of concentration or energy use, because she went right back to her normal Beam Spam right afterward.
 * Thundarr the Barbarian's Sun Sword could cut through inanimate objects and Mecha Mooks as if they were tissue paper. But the moment he tried to strike down a living foe, the Sun Sword inexplicably didn't work. (At least the writers lampshaded this by having Thundarr express surprise, dismay or both at this.)