In most fictional universes (and Real Life), things tend to function in a particular, expected way, and perform that function consistently. Phasers have settings, Shur Fine Guns will go off when the trigger is pulled (and sometimes when it isn't), healing potions will heal, and cars will ignite as they fly through the air.
But sometimes the plot calls for an item to operate in ways that weren't previously established. This effect can be unexpected, to the point of feeling like an Ass Pull, or outright inconsistent with its previous known functions. But it'll get you through to the next plot point, and that's all that counts.
A classic example is time bombs, which will go faster or slower depending on how much tension is needed.
When a writer attempts to explain the sudden change of behavior, he/she will frequently invoke Phlebotinum Breakdown, or Retcon the function into the item's repertoire. The way to tell, frequently, is by watching to see whether this new old function appears again.
If the change of function is not merely a handy means to an end, you may instead have Chekhov's Gun—particularly if the characters notice or should have noticed.
- Almost Lethal Weapons
- Cell Phones Are Useless
- Context-Sensitive Button is for control panels
- My Car Hates Me is vehicle-specific
- Plot-Sensitive Button
- Plot-Sensitive Latch
- Super Cell Reception is phone-specific
Sister Trope of New Powers as the Plot Demands, the superhero version. Compare Suddenly Always Knew That. Not to be confused with Magic Tool and Green Rocks, both of which are known from the outset to have multiple and possibly unknown functions, or the Swiss-Army Weapon, which can explicitly do just about anything if you know how to use it.
Remember, this is about a specific "normal" item acting strangely; do not add examples of all-purpose Phlebotinum like Star Trek's "reverse shield polarity" and "deflector pulse" or Doctor Who's sonic screwdriver.
Examples:
Anime & Manga
- JoJo's Bizarre Adventure: The Stand Arrow is introduced as being the method of acquiring a Stand. Near the end of Diamond is Unbreakable, it suddenly acts on its own to grant Bites The Dust to Yoshikage Kira. In Golden Wind, it is revealed piercing a Stand with the arrow evolves it further to become a more powerful version called Requiem.
Comic Books
- Wonder Woman: Pre-Crisis the abilities of Diana's lasso were subject to change to make a story work, but this was fixed in Wonder Woman (1987) where the lasso's abilities were clearly defined and kept to for decades until the '90s wanted things darker and edgier. Its first and second shown abilities in the Post-Crisis continuity went absent without explanation causing Diana to have to kill Maxwell Lord when wrapping him in the thing should have caused him to drop his flawed plan instantly (if not necessarily permanently) like it had done previously to gods.
Films — Live-Action
- The Call: When Jordan arrives at the place where Casey is being held, her phone appears to have no service. However, when the former rescues the latter at that very spot, she attempts to call 9-1-1, as if she now has cellular service. Additionally, the former drops her phone into an underground murder lair. Cell phones don't work well underground.
- The Kindergarten Teacher: The lock on the hotel's bathroom door is highly unusual in that it locks from the outside only, therefore allowing Jimmy to trap Lisa inside. Not typical of how most locks on bathroom doors work.
- Visual Comedy: An object can become funny by behaving in an unexpected way, as demonstrated by a banana suddenly bending.
Live-Action TV
- Buffy the Vampire Slayer:
- Sunlight burns nameless mook vampires faster than the recurring ones.
- For that matter, Buffy can hit a Mook vampire anywhere in the torso and he'll turn to dust, staked through the heart. It's a plot point in Season 2 when a named vampire is shot with a crossbow bolt barely missing the heart, and it's *much* closer than it normally takes for Buffy to kill anyone.
- Doctor Who: In "Wish World", it was revealed that the Vindicator, having gathered power equivalent to a billion supernovas, amplified the effect of Conrad's wish on Desidirium. "The Reality War" reveals it can be used as an Energy Weapon—just what's needed to stop Omega.
- Salvage 1: The Made of Explodium monohydrazine was used to solve any number of problems, from fueling a rocket to restarting oil wells.
- Stargate-verse:
- The Stargate closes just before someone "unwanted" is about to enter it and sometimes it allows them to go into the orifice. Sometimes it just stays on or closes for no apparent reason. It's a complete mess in what's otherwise a decent universe.
- The zat guns too, although in this case, it may be a subversion since they just kind of lost an ability. The rule at the beginning of the TV series was: first hit stuns, second hit kills, third hit disintegrates. It was an excuse to get rid of any inconvenient bodies that they didn't want to keep track of. The creative team eventually decided it was stupid, and the ability just kind of vanished. This was lampshaded in the 100th episode "Wormhole X-Treme".
- Star Trek: More to the point, the Main Deflector Array has been used to do just about everything. It's even the go-to choice when you want to do a one-shot overloaded weapon attack. It does more damage than the actual weapons would.
- Supernatural: In "Scarecrow", the victims have their car breaking down and no cell phone reception. Possibly justified as the townspeople deliberately made sure the former happened and likely would have worked to ensure they ended up in a dead zone for the latter.
- Viper: The EMP gun can shut down an engine and make it almost uncontrollable, but if you hit a human with it, it just tickles you.
Toys
- BIONICLE: The Mask of Life. Need to get rid of a bad guy in a family-friendly manner? Mask turns him into a snake. Need to sell more toys of the same characters and give an explanation as to why they look different? Mask upgrades them into new forms. Need to seal the Great Spirit away somewhere? Put him in the mask, etc. There's also Energized Protodermis, which will either transform or destroy the victim depending on their destiny.
Video Games
- ANNO: Mutationem: The Grom System is initially designed as an Everything Sensor to search for obtainable items and examine the map. It then later becomes able to perform hacking to open locks and scan for Fluorescent Footprints to track down a specific person.
- Ratchet & Clank: Many of the gadgets in the franchise fit the bill.
- The Electrolyzer from Going Commando can fix nigh anything, with any technical fault, just by spinning a few dials to allow a current through. Anything from a hoverbike, to a computer terminal, to a Broken Bridge.
- The Hypershot from Up Your Arsenal can not only activate floating platforms but can also extend an energy-based grappling hook to latch onto Versa-Targets.