Unpredictable Results

""What do you mean, 'it breaks reality?'" "I mean you turn it on, and reality breaks.""

- The Skeletor Show

The notion of unpredictable results has long been an easy source of intrigue on television. Its most common form is the exotic technology or mysterious mythical artifact. Often the in-character source of a Deus Ex Machina.

Sometimes a source for drama, where the sudden, unexpected result can either give the heroes something to fight and/or resolve, or save their hides. Othertimes, used for comedy; "either it will cause peace and happiness throughout the land, or plunge us all into complete pain and fear. We're not sure."

Essentially, the opposite of Functional Magic.

Comics

 * Red kryptonite has unpredictable effects on Superman which last for forty-eight hours and are never repeated. As the essay The Well Tempered Plot Device puts it, this means the writer can try on any daft idea they like with no effect to the comic's continuity.

Film

 * Galaxy Quest and its Omega-13, though its results are successfully predicted near the end.

Literature

 * In John and Dave and the Temple of X'al'naa'thuthuthu, the sequel to John Dies at the End, the Furgun embodies this trope. Technically it does whatever the user wants it to do, but getting the result right is finicky. It's as likely to enlarge things as it is to turn them into mashed potatoes, blow them up or give them beards. When the narrator tries to defend himself with it, the mental image of an old painting of Jesus flips into his mind, so the painting pops out of nowhere and starts shooting lasers out of its eyes. When he has an urgent, urgent case of Kill It with Fire, he does all he can to imagine flames as he pulls the trigger. Nothing happens. Then there's a streak of light in the sky...
 * The Wild Card virus.
 * Collapsing a hypergate in The Lost Fleet can cause an explosion anywhere between "tactical nuke" and "supernova".

Live Action TV

 * Buffy the Vampire Slayer, episode "Earshot", where Buffy is stung by a demon and learns only that she will gain an "aspect of the demon", which could be anything (it turns out to be telepathy).
 * Alias was particularly ambitious with this trope, basing an entire arc around exotic "we don't know what it's for" technology.
 * The neurotransmitter Promicin, in The 4400 is described as unpredictable—somebody injected with it will either gain a superpower or drop dead, and there is no way of predicting what that will be.
 * In Lost's season 4 finale, is said to be "both dangerous and unpredictable" (partly to explain why it wasn't done before.) We know it resulted in
 * Now we do, sort of, it . It's complicated basically.
 * A Disclaimer on Ned's Declassified School Survival Guide is "Your Results May Vary".

Radio

 * The Heart of Gold's improbability drive in The Hitchhiker's Guide to the Galaxy works by producing a near-infinite number of unpredictable results and then "picking" the desired one (usually going from Point A to Point B) and sticking with it. Of course, the temporary side effects of engaging it (such as turning into a penguin or generating sperm whales) aren't exactly pleasant.

Tabletop Games

 * The roleplaying game Dungeons & Dragons has the Wand of Wonder (the Rod of Wonder in later editions)-- a magic item whose effect is randomly determined from a table of 50 or so possibilities each time it's activated. Possible effects range from shooting fireballs to turning a random combatant into a rhinocerous, and a popular pasttime on the game's official forums is coming up with new and even more bizarre effects for the item.
 * Wild magic in 2E could have similarly unpredictable effects.
 * This troper once used this unpredictability in what he considers a CMOA during a sanctioned tournament by telling the designated antagonist that had just ambushed them that either everyone walked away unharmed, or he would begin rapid-firing his Rod of Wonders, and did the Designated Antagonist feel lucky today, punk?
 * This troper is currently playing in a homebrew setting where any spell has a one in twenty chance of having a random effect. Great when it gives everyone in the party a buff. Not so great when it turns the sorceress to stone.
 * An even more powerful but similar item is the Deck Of Many Things, where any card you draw can have really good (you gain a powerful magic item, a fine warhorse, or a small castle) or REALLY BAD effects (you lose all your money, your good reputation, YOUR SOUL...). It's been nicknamed "Total Party Kill in a can" for good reasons.
 * This troper once decided to let his D&D party stumble upon said Deck, assuming the players would be wise and use it with moderation. It didn't work out that way. The druid of the party ended up getting a grown up, unwanted daugther out of nowhere, and that's the least absurd of the results.
 * This troper once had a GM who decided to toss a modified Deck of Many Things at the party, with the warning that it had been modified and some of the negative effects might be worse. And these were experienced players, too. We used it (although most of us managed some kind of moderation): one of the players ended up a different class; my character ended up with Fertile Feet as a side-effect of being a newly-minted avatar of a goddess of love, along with a repaired artifact weapon; and one guy ended up with the power to shift into any creature he wanted with 6d10 worth of hit dice. Then, of course, the last girl drew the whole deck in one go and ended up with some neat rewards that were promptly negated by drawing the worst card in the deck: she lost all her gains up to that point, negated anything she would've gotten past that card, and had her soul ripped out and tossed into a prison dimension with the only hope of escape being the party going on a very extended quest (and even if she had managed to avoid that fate somehow, her next roll would have required her to fight Death. She would not have won).
 * Previous versions of D&D had a LOT of utterly random effects, usually as dungeon features. The module "In Search Of The Unknown" had a set of magic pools whose effects when drunk changed with every sip.
 * Enter the Mists of Ravenloft without a Vistani guide, and you could find yourself wandering for any amount of time, from minutes to months or (rarely) even decades. Likewise, you could end up in some other Ravenloft domain, come right back to where you started from, be dropped off on your world of origin (if you're an outlander and your DM is merciful), or even get deposited on a completely different D&D campaign world from your own.
 * And while you're wandering around in there, you could encounter literally anything along the way.
 * Exposure to Chaos in Warhammer Fantasy Battle yields unpredictable mutations, which in extreme cases can turn the character into a midless gibbering Chaos Spawn.
 * Warhammer 40,000: Anything connected to the Warp or Ork technology. Represented ingame by psykers suffering "perils of the warp" attacks and more esoteric Orky wargear having its own tables of random effects. Ork psykers are beyond random, rolling just to see what completely-unpredictable power they get... every turn.
 * Beware if you play as a Necromancer in the Furry Fandom version of D&D, Ironclaw; if you try to cast a spell, and you roll at least 3 6's, you'll get hit with a magical backlash that does totally random (but always negative) things. In fact, the official rulebook encourages dungeonmasters to get as creative as they could with what happens.
 * Magic is like this in GURPS. When it fails it does so in extremely random ways. There are at least six different official tables of backlash effects ranging from "Black Magic" (which results in Body Horror) all the way to Cosmic Humor (which causes reality to mock you in the most painful way it can).
 * Any casting in FATAL, with possible miscast effects including "caster thinks he's a cat" (funny), "caster becomes a serial rapist" (not funny, but apparently intended to be), "caster gets raped by gay ogres" (Dude, Not Funny) and "accidentally casts F.A.T.A.L." (a wonderful chance to play a different game).
 * The various shipboard items used to fight The Awful Green Things From Outer Space might injure them, cause them to grow, or do nothing at all, completely at random. However, any specific item continues to have consistent results once it's been used.
 * Red mana in Magic: The Gathering is the color of randomness, chaos and unpredictability. Most of the time that appears in the form of cards that happen to interact like that; for example, creatures attacking the turn they come into play and changing the targets of other effects are both red abilities, and both result in unpredictable game states, especially for your opponents. Some effects, though, genuinely require players to randomize things, such as by flipping a coin or rolling a dice. In its most extreme form, the card Scrambleverse will assign every card in play to a new controller chosen at random.

Toys

 * Bionicle's Unobtainium, Energized Protodermis either transforms all that comes into contact with it into whatever its destiny calls for, or simply destroys it. This goes for everything, from objects to living beings. Then, there are the Reconstitute at Random Kanoka Disks, which transform their target into who-knows-what, Teleportation disks, which teleport the targets to random locations, and the Mask of Summoning, which summons random creatures whom the mask's user unfortunately has no control over.

Video Games

 * The Lab Ray in Neopets, which can add stats, take them away, change species, or even change gender.
 * The Pokémon attack Metronome, which allows a 'Mon that knows it to perform almost ANY attack at random.
 * There's also the slightly-more-controlled Assist/Cat's Paw, which randomly uses a move from one of your teammates' movesets.
 * In Dungeon Crawl Stone Soup one can worship the god Xom, who can do essentially anything to you on a whim, good or bad. The probability of getting a good effect is raised by how amusing Xom finds you at the moment- and the easiest way of amusing him is by doing things that have random and potentially disastrous outcomes, like drinking unidentified potions.
 * The Wand of Wonder from Baldur's Gate strikes whoever its pointed at with a random effect.
 * Who could forget the Wabbajack? A magical staff from Oblivion that turns a creature into a random creature.
 * ADOM has magical pools which can be drunk from for random effects, from being cursed, to being turned invisible, to gaining a wish.

Webcomics

 * A major arc of the webcomic Its Walky centers around this. The Head Alien uses a machine to stop time in Canada (Citing his reason as, "I figured, who the heck would notice? Damn if I wasn't right...") in order to trap a demigodly alien known as 'The Cheese'. However, overuse of the time-stopping device creates unpredictable results, such as reversing the gender of everybody in the vicinity, giving somebody a Funny Afro, or turning him into a Pirate...
 * In the webcomic Tales of the Questor, Quentyn's magic sword, Wildcard, could go from unstoppable to useless with every attack due to the unique way it was first charged (A night of drunken spellcasting by Quentyn and his friends).
 * Roughly 50% of Riff's inventions in Sluggy Freelance work like this. The Dimensional Flux Agitator has a particularly spotty record.
 * The shield from Goblins, which has a massively varied number of random effects when struck.

Web Original

 * SCP Foundation-914, AKA "The Clockworks" is entirely based on this, as is SCP-261, a profoundly unpredictable vending machine.

Western Animation

 * In an episode of Pinky and The Brain, The Brain warns Pinky never to use more than one drop of his shrinking serum, because "it would cause a reaction on the molecular level that is completely unpredictable"; the reaction turns out to be turning people into huge yodeling clog dancers.
 * The Allspark and the key it empowered in Transformers Animated, which apparently has a mind of its own.

Real Life

 * Truth in Television: Change just one line of a sufficiently complex piece of code.
 * Segmentation Fault. Core Dumped.
 * In C/C++ the language standard allows for "undefined behavior" for some operations (e.g. accessing an array beyond its bounds), leading to the Jargon File's "nasal demons" joke.