Defeat Equals Explosion

"If I become an evil genius, I'll keep in mind not to replace my blood with nitroglycerin, hydrogen or any other flammable thing, I don't wanna die exploding like the bosses of Ninja Gaiden."

—Payasoplas, on Ninja Gaiden

Sometimes an enemy being defeated just... explodes. Not metaphorically like in the Villainous Breakdown sense, but in a literal, physical explosion.

In the case of robots, this could be justified, as the defeat would probably cause them to short circuit and the spark to ignite their fuel. But this is not limited to robots, since this happens with characters who are not specifically stated to be robots, and in some cases are implied to be organic in some way or another.

Having every enemy explode upon death was more common in the 3rd and 4th generation of console gaming, when it was mainly done to avoid drawing death animations. If an enemy's express purpose is to deal damage by actually exploding, then you have an Action Bomb. Similarly, if an already-defeated enemy pulls this stunt to try and inflict some last-minute damage, it's Taking You with Me.

Examples of Defeat Equals Explosion include:

Anime and Manga

Dragonball Z: This happens a lot. Lampshaded in Dragon Ball Abridged by Team Four Star:

(Vegeta hits the ground, large explosion. Later, he crawls out.)
Vegeta (gasping): Why did I explode?

Evangelion all the way. When the Angel's cores are destroyed, they explode and leave a lake of red gunk.
Fist of the North Star: Except with blood, guts (or just liquid light in the anime). And mostly with mooks.
Sailor Moon: Most Monsters of the Week end up this way, particularly in Series 1. Or crumbling to dust, but mostly after exploding in a flash of light.
Exaggerated in Panty & Stocking with Garterbelt, where the defeated demons not only explode when defeated, but also undergo Art Shift before exploding.

Film

Return of the Jedi: The evil Emperor apparently explodes on impact after being thrown down the shaft at the climax of the film.
In the Wes Craven film Cursed, when the werewolf who infected all the other major characters dies, he inexplicably explodes in a burst of greenish energy.
Double Team: In perhaps one of the most awesome endings to an action film: The Bad Guy (played by "Mickey" Rourke) is left standing on an armed mine, with a Tiger, in the middle of a Colosseum. Just as the Tiger is about to claw him, he steps off, where the whole place explodes. Completing the total madness, Jean-Claude Van Damme, Dennis Rodman, and the actor who played Belloq outrun the ensuing fireball, hiding behind a Coke machine, while carrying a baby!
Some of the Godzilla films has the enemy monster explode after the titular monster kills them. The early films don't do this however.

Literature

Demons in Dark Heavens.
Before the prequel trilogy came out, the Star Wars Expanded Universe almost universally had dead Jedi fade away while dead Dark Jedi or Sith exploded violently the way the Emperor did. Later it was retconned into a power they had, a kind of Taking You with Me thing. In the Hand of Thrawn duology, Mara Jade once makes this sardonic remark when she's in need of explosives.

"Too bad we don't have a Dark Jedi handy we could kill. Remember that big blast when C'baoth died?"

Live-Action TV

When you think of this trope, you probably think of Power Rangers first. When the Monster of the Week eats the Finishing Move as the theme song plays, he goes up with an impressive fireball. The whole Tokusatsu genre in general employs this - from at least the 70s onward, Kamen Rider, Super Sentai, Ultraman, Metal Heroes and many more have had monsters that go out with a bang.
- Sometimes the background explodes just because Pure Awesomeness is Volatile. Power Rangers especially. And sometimes, the Rangers will turn and pose after the Finishing Move so the explosion behind them will look like one of these sequences.
  - At least once, doing that didn't pay off: once in Power Rangers Dino Thunder, they blast, then turn and pose... and the monster wasn't dead, and blasted the Rangers in the back.
- Also, despite this trope, every series will have the heroes think a monster dead without seeing the customary kaboom at least once. This counts as Genre Blindness bordering on Too Dumb to Live.
Message from Space: Galactic Battle has all major enemies explode. One even tries to destroy a MacGuffin with his death explosion.

Tabletop Games

Dungeons & Dragons.
- In the Dragonlance setting both Aurak and Bozak Draconians explode when they die.
- Killing a Balor for good in the Abyss results in a quite dangerous explosion. In AD&D2, it's 50 hp (save for half) of unspecified type, in 3.5, it's a ball of fire that deals 100 points of damage.
- The balor is topped by the nuclear elemental from d20 Modern, which exploded for 1000 points of untyped damage in a five mile radius. (Reflex save for half).
  - Of course, in d20 the Reflex Save for half allows anyone with Evasion to dodge the blast entirely (barring special rules).
Villains and Vigilantes adventure Devil's Domain. When the Player Characters kill any of the Devil's demons, the demons explode in a cloud of noxious brown smoke.
Common in Warhammer 40,000
- The prime culprit in the tabletop game itself is possibly the Eversor assassin, whose unstable chemical cocktail of a body literally explodes upon suffering sufficient physical trauma, usually taking with him whatever he was fighting at the time.
- Pretty much any vehicle, though probability depends on the game line and edition.
  - The real killers are the Super-heavy units in the mass-combat expansion Apocalypse. They'll often take out entire squads if they explode, even if the squad(s) in question wasn't even in close combat with it. Titans have a special rule called "reactor meltdown" which causes them to explode with an even bigger blast that's also strength D (auto wound or penetrating hit on anything in range). An exploding Titan can take every unit on the board with it!
- In Battlefleet Gothic and Rogue Trader possible results of catastrophic damage (destruction of spaceship or space station) include plasma drive explosion, which causes fireball the size of a small moon. The ones capable of Warp travel may open a Warp rift instead, in which case everything nearby gets sucked into Hell.

Video Games

Metroid: Most bosses in the series will explode. This is somewhat problematic for recurring bosses such as Ridley, who has managed to come back from complete annihilation several times throughout the series.
The Cobras in Metal Gear Solid 3: Snake Eater all die by going boom... except The Boss. In this case, it's explained that the Cobras were equipped with microbombs that would explode when they died, in order to prevent the enemy studying their corpses.
All the enemies in Beyond Good and Evil. Exploding on death must be a quirk of the DomZ's physiology.
Any player in Quake III: Team Arena and Quake Live who dies while carrying the Kamikaze holdable powerup. When dying, (and if they're not gibbed) they will produce a huge explosion which shakes the arena.
Unreal Tournament: The carrier of the Vengeance Relic in matches with the Relic mutator will explode violently upon dying.
In Half Life, any Gargantuas you encounter (the big, hulking aliens that shoot fire at Gordon) will die with a chain of explosions whenever killed.
Mega Man: Just about every enemy explodes upon defeat; partly justified in that they're robots, but an explosion happens regardless of whether or not the type of weapon used would logically cause an explosion or not. (For instance, Storm Tornado in Mega Man X). The only enemies that doesn't explode is Proto Man, he simply stops and teleports out of the arena (though arguably he really isn't an enemy) and Dr. Wily (the machine he's piloting does though) because he falls out and surrenders, heck even Mega Man himself explodes into a billion energy orbs when his bar thingy with about 28 other bars...runs out.
Some boss enemies from Jazz Jackrabbit go boom when killed.
In God of War, the giant lava minotaurs explode when defeated.
This happens to all the bosses in the Mario & Luigi' series', even if they are alive in the cutscene that follows.
In the Shinobi series, all enemies explode when they die.
Shining Force III had enemies explode when killed.
The Legend of Zelda the Wind Waker: All monsters explode into ominous (yet harmless) purple smoke. Except for the giant Armos Statues, who explode like bombs and does damage when you are too close to the explosion.
The lambent locusts in Gears of War will explode when they are killed. This was justified by their exposure to the emulsion.
The one-hit enemies from Contra series get knocked back shortly before exploding.
The weapon in Moon Crystal makes every enemy explode into 4 waves when hit enough. Even bats and all kinds of monsters.
All the enemies in ActRaiser series.
The enemies in Kirby series tend to explode with puffs of smoke and pentagram-like shapes.
In NES Ninja Gaiden games, ordinary enemies explode into 4 fiery waves expanding diagonally.
Enemies in Blaster Master enemies meet the same fate.
Sword in Strider series makes them go boom!
Enemies in Ghosts N Goblins series explode too without any given explanation.
In La-Mulana, enemies go down that way.
Enemies in Mole Mania die in a very corner-y explosion.
Gremlins 2, every enemy does a Chain-Reaction Destruction upon death.
Every enemy explodes in Mushihime-sama series too despite most of them being insect-based.
In Gunstar Heroes, the enemies, whatever they might be, explode.
In some of the Castlevania games, enemies explode upon death or leave a small flame.
In Run Saber, almost every enemy seems to explode upon death.
In Silver Surfer NES game, same thing.
Star Fox 64 is a wonderous explosionfest.
Makes sense for tanks and airplanes in Advance Wars. But foot soldiers? Not so much.
Enemies in Gods explode.
Enemies in Earnest Evans.
Everything you can pick up (including enemies) in Superman 64 explodes. Even boxes.
In the Mechwarrior series from 2 onwards, most enemies have a tendency to explode when destroyed, instead of perhaps just falling over or remaining upright but deactivated. In 2 and 3, any mobile or aggressive target usually ends up disappearing in a sizable explosion and polygonal bits when destroyed. This includes 'Mechs, tanks, aircraft... even Elementals - humans in Power Armor. In Mechwarrior 2 and even in Mechwarrior 3, they explode into a fireball several times the size of the original armor suit, in spite of the fact that according to the games, they can't be carrying nearly enough in them to explode like that. 'Mechs on the whole seem suspiciously prone to exploding as opposed to anything else.
- Destroying a 'Mech in Mechwarrior 2 usually causes it to explode violently, sometimes remaining visibly intact only for the pieces violently fling themselves across the screen. The occasional 'Mech will remain on the field as an armored, intact hulk (which can be shot apart), usually as a result of a cockpit hit. Some 'Mechs played the explosion animation close to 10 times after being destroyed, and some would even do so long after the pieces had been blown across the map.
- In Mechwarrior 3, 'Mechs and vehicles explode when they were destroyed, with 'Mechs bursting into flames and flopping over when destroyed. The only exception was for a 'Mech killed with a leg hit—these would just fall over and crash on the ground, disabled and out of the fight. To make up for this lack of pyrotechnics, one could cause a fusion plant explosion by the simple expedient of overheating a 'Mech, yours or theirs. Obviously, anyone close enough to witness these were usually not happy about it.
- In Mechwarrior 4, some vehicles will simply turn into skeletal outlines of their former selves when destroyed, and aircraft usually cause a small explosion when shot down. Fairly reasonable, all things concerned. However, every defeated 'Mech violently flings itself to the ground and then goes critical with a blown reactor, no matter what kind of damage destroyed it—a shot through the torso, both legs blown off, or a cockpit hit. The end result is invariably a chunky 'Mech-shaped pile of burnt debris, looking every bit like a total loss. The tendency for every 'Mech to do this raises questions as to how your technicians manage to salvage equipment and weapons off these blown-up remnants...including entire intact, viable 'Mechs.
Every single boss in Skies of Arcadia goes up in a fiery explosion after you defeat it. For the ship battles, this makes some sense. But when it's a giant hollow Jello monster filled with poison with skulls floating around in it? Or what appears to be a gigantic evil toucan? They explode about as violently as the ships do.
In City of Heroes, Council drones, some Arachnos spiderbots, and at least one variety of Praetorian clockwork explode when you destroy them.

Webcomics

In The Beast Legion, Gorgorath goes through this in Issue 4.