Kill One, and the Others Get Stronger

A group of characters, usually antagonists, who seem to have a shared pool of personal power, distributed among all living members. If one of them is killed, the others become proportionately stronger, making the last of them the most powerful of all, regardless who it ends up being. Provides a natural enemy challenge escalation for the protagonists.

Not to be confused with Victor Gains Loser's Powers (where the victim's power goes only to his killer) or Unstoppable Rage triggered by the death of a comrade (this trope is about quantifiable increase of power, not psychological affect). Awareness of this trope can lead to a There Can Be Only One motivation. Compare Conservation of Ninjutsu for when smaller numbers inherently equal more competence and Level Scaling for when a character becomes stronger, his foes grow stronger with him.

Comic Books

 * in Rising Stars, this is eventually discovered to be true of the Specials.

Film

 * In The One, life energy is distributed equally among all versions of the same person across 125 parallel universes, meaning that the more of them die, the stronger and faster the remaining "copies" become. The antagonist is actually one of said copies, who has been killing the others for their power.

Literature
"They rove in small bands, and within those companies the death of one man only adds to the strength of all the rest...the more you strike down, the more the others gain in strength. Even as their number dwindles, their power grows."
 * In Arcia Chronicles, the Horsemen of the Apocalypse grow individually stronger when one of them is killed, which is why Erasti is reluctant to fight them.
 * Prydain Chronicles. The Huntsmen of Annuvin have this quality. Prince Gwydion describes them in The Black Cauldron:


 * The mutated wyrsa seen in The Silver Gryphon got smarter as each pack member was killed.

Tabletop Games

 * A Dungeons & Dragons version of the Prydain Chronicles Huntsmen of Annuvin appeared in Dragon magazine #40. Each time one of them was killed, his original Hit Points are divided among all of the surviving Huntsmen, making them more difficult to kill.
 * A borderline example in the Deadlands setting Lost Colony. You can fight the four Big Bad demons but each time you kill one, a fifth demon will absorb the power of the killed (unless you thwart his plans first) and become stronger until he absorbs all their powers combined.

Video Games

 * In the 2008 Prince of Persia, the remaining Corrupted bosses grow stronger with each Corrupted the Prince and Elika defeat for good.
 * In Space Invaders, the more enemies you shoot, the faster the survivors become.
 * By extension, this applies to any game where the sheer number of enemies lags the system enough to slow all the enemies down. As you kill them, the game stops lagging, making the remaining enemies faster (up to a point).
 * Happens in Clive Barker's Undying to the Covenant brothers, according to Word of God. Bethany, the last to be killed, certainly had created a good army of creatures prior to her death.
 * In Dungeon Crawl, you might run into elven twins, Dowan the mage and Duvessa the fighter. While killing Dowan first merely results in Duvessa's berserking (a non-permanent bonus to speed and strength), killing Duvessa first makes Dowan's spellpool instantly expand to include devastating new spells for no apparent reason.
 * The Godbeasts in Seiken Densetsu 3 can be fought in any order (with the exception of one which is always fought last), but each time one is killed, the others and the monsters living in their lairs grow in power by a few levels.
 * Certain mobs in Star Wars: The Old Republic have an ability to grand a (semi-permanent) powerup-status to nearby allies when they are defeated, which is described as this trope—basically, they're so heroic that seeing them fall just makes their allies fight even harder. Large groups of them, while rare, can be quite hazardous...
 * In Phantom Brave and Makai Kingdom, whenever an enemy unit is tossed out of bounds, any surviving enemies get an increase in level.
 * World of Warcraft features a raid boss battle against a group of three enemy generals known as the Assembly of Iron; as each one falls, they unleash a unique power called Supercharge which increases the damage that the survivors do by 25%. When only one remains, they receive a nasty new ability. Raids must choose the order careful, lest they find themselves swiftly overwhelmed by the power the last one standing possesses.
 * City of Heroes features the Vengeance power, which provides a powerful and relatively long-lasting team wide buff when cast on a defeated ally. The version of it used by Lieutenant-level members of the Nemesis faction might be a better fit for the trope, however - they are able to unleash the power as they are defeated, described in game as the loss of a good leader enraging the team.
 * Supervillain Red Sun in Freedom Force vs. The Third Reich has the ability to exist in several bodies at once. When you defeat one, not only do the rest become stronger but also heal.