Powder Trail

"Ahah! Zis is an example of smartness. I have said zat zis is ze kvick fuse, und zis is ze kvick fuse! ...Ze kvick fuse!?!"

—Franz Liebkind, The Producers

Similar to Vapor Trail but generally with a different intent.

A trail of gunpowder is laid as a makeshift fuse, leading to a pile of explosives (usually barrels of gunpowder). Once lit, the trail smokes and sparks impressively and the hero will have to race the burning powder to scuff out the line before it reaches the explosives. In a comedic variation, a character will unknowingly leave a trail of powder behind him as he is stockpiling explosives, allowing another character to casually light it, blowing the first character to kingdom come.

Tested and confirmed by the MythBusters. This is one of the few explosive myths they've tested that worked in real life pretty much exactly the way it is portrayed in movies. And, just like the movies, it was also possible for a person to outrun it or just scatter the trail.

Examples of Powder Trail include:

Anime and Manga

Pokémon did this in "Attack of the Prehistoric Pokemon", but with a really long fuse line leading to a stack of dynamite (I'd say it was smart of Team Rocket, but they ended up following Ash anyway to stop the defusing). One pile-up later and it all goes to naught, however, as Pikachu zaps the entire load. "Chaaaaa..." indeed.

Comic Books

Gaston Lagaffe once accidentally left a trail of his home-made rocket fuel behind and unknowingly lit it. The running fire ended up igniting the Mesmaeker's contracts.
Pulled off in issue #78 of the original series of Jonah Hex, where Jonah ignites the powder trail with a rifle shot.
The cover of Knights of the Dinner Table Special Edition #1, as seen in the page image.

Film

In one of the first color movies of all time, The Black Pirate, the villainous pirates use this technique to blow up ships after they have left.
In the movie The Return of the Musketeers, the powder fuse is used to blow up a ship.
Used in film The Mask Of Zorro.
B-Movie Ator The Invincible ("Cave Dwellers" on Mystery Science Theater 3000) had a character do this with rock dust. Cue the guys: "She's making flash powder out of her own filth!"
Muppet Treasure Island. Freaking hilarious, Rizzo and Gonzo scared witless trying to load a gun to fend off pirates.... Kaboom!!
- Not to mention the sparks follow them as they try to escape.
  - That's because they still had the leaky barrel of powder under Gonzo's arm.
In the first Pirates of the Caribbean, the Black Pearl crew does this in a ship. Though it was rather elaborate, running along a board over open water, on an already sinking ship, which makes one wonder how the hell did it not get wet or lose a critical few inches halfway through...
As indicated by the page quote, in The Producers, the protagonists come to regret using one of these.
- Although that is an actual fuse rather than a powder trail. The end result is the same.
In Cutthroat Island, the Mexican Standoff in the tavern between Dawg's men and Morgan's men is broken when Shaw removes the cork from an enemy pirate's powder-horn. Bowen sees him do this and tosses him a lit candle. The other pirate takes a few steps away, and Shaw drops the candle, literally starting off the ensuing fight scene with a bang.
In the comedy western The Villain, Cactus Jack accidentally creates one of these, and has to be saved from being blown up by his horse Whiskey.
In It's A Mad, Mad, Mad, Mad World, this is one of the many methods by which the Crumps attempt to escape from the hardware-store basement in which they have been accidently locked.
Leon (Anthony Quinn) uses a powder trail to blow the dam and drown the attacking Indians in Guns For San Sebastian.

Literature

Happens in the Animorphs book Elfangor's Secret. The villain plans to destroy HMS Victory during the battle at Trafalgar, and uses the powder trail to give him extra time to make his escape via Time Travel. Ax managed to cut the Powder Trail in the nick of time, using his tail blade -- only to accidentally strike a spark that ignites the rest of the trail.
In the fourth Gotrek and Felix novel, the dwarfs lay a powder trail (and a couple kegs of powder) to collapse the tunnel leading into a dragon's lair in case they're overrun by orcs or bandits. Their engineer's rocket launcher accidentally sets it off, leading to much swearing since the dragon had quite a large hoard.
Used by Richard Sharpe to destroy a friendly fortress in Sharpe's Gold.
Solomon Kane uses one to kill the majority of Le Loup's gang in Red Shadows.

Live Action TV

Done on Lost to open the hatch.
MacGyver improvises a powder trail to blow up an arms shipment in "The Escape".
A staple on the various Zorro TV series.
The Queen uses one to set off an explosion that collapses a mine (and allows her to escape the soldiers in the ensuing confusion) in the Queen of Swords episode "Death to the Queen".
Miss Fisher's Murder Mysteries: In "Framed for Murder", the murderer uses a long line of celluloid film like a powder trail to ignite a huge pile of unspooled film he is planning to use to burn his victim to death.

Video Games

In The Curse of Monkey Island, Guybrush knocks over a keg of rum, leaving a trail of the alcohol down the grassy knoll and to the keg, which happens to be sitting next to a rubber tree. He lights the trail with a match (would work since pure rum is flammable), and proceeds to be blown right off the cliff and into town by the blast. After coming to, he drowsily declares, "Woah, my head is spinning. I gotta lay off the rum!"
One mission in Sly 3: Honor Among Thieves has General Tsao doing this to a captive Murray. Penelope uses one of her RC cars to save the day.
In Time Splitters 2, the player character is required to do this to get an NPC out of a wild west jail. One must create a powder trail from underneath a lantern inside the jail to a wagon loaded with powder barrels pushed against the wall outside, then shoot the lantern off the ceiling.
- You what? I always just shot the barrels. When they exploded, they lit the trail.

Western Animation

The comedic variation happened frequently to Wile E. Coyote and Yosemite Sam in Looney Tunes shorts.
- Also to Tom of Tom and Jerry.
- It's one of the many penalties in "Early to Bet," #36: Roll out the Barrel.
Jonny Quest TOS episode "Riddle of the Gold". Bandit saves the day by putting out the flame with his...err, tail. :)
- Race hangs a lampshade on it even then: "Isn't that a bit of an old routine?"
The Hooded Claw uses one in an attempt to dispose of Penelope in The Perils of Penelope Pitstop episode "Jungle Jeopardy". This works about as well as any of the Hooded Claw's schemes do.
The Adventures of Tintin features this. Sir Francis Haddock sets it off, Red Rackham snuffs it out, repeat, repeat...

Real Life

Such powder trails are Truth in Television, as this was a common way of setting off early cannon on land (back when there was a real chance of explosion so you did not want to stand near it when you fired it; not believing that one was needed was what did it for King James II of Scotland.)
Truth in Television: Guy Fawkes was caught making sure the gunpowder trail leading to the explosives he planted under the house of parliament were perfect before lighting it.