The Dark Arts

"Spargel: Elzar had been seduced by The Dark Side of cooking. Cilantro, mango salsa, raspberry vinaigrette!

Bender: That drizzler!"

- Futurama, "The 30% Iron Chef"

Basically, The Dark Arts are any science, discipline, magic or martial combat style that is deemed by society in general and the establishment in particular as a Bad Idea.

In other words, if there are Things Man Was Not Meant to Know, you can expect someone to have thought it would be cool to make an easy to read how-to book on it. The "Dark" Art might not necessarily be evil or dangerous, but there's always at least some cause to consider these powers/skills potent and not to be left open for everyone to learn.

This can be for any of the following reasons, sometimes several at once:
 * It's very dangerous for the practitioner and those around him, usually because it is:
 * Explicitly evil and corrupts the practitioners.
 * Has a really ghastly price to use.
 * Can only be obtained by evil activities.
 * All its Potential Applications are destructive.
 * All the products end up Going Horribly Wrong. Robots rebel, resurrections are botched, superpowers cause insanity. Basically, if you can build a Fantastic Aesop out of it, it's this.
 * The Dark Art represents a threat to the establishment because it:
 * Looks really scary, or a small but dangerous band used it. Usually the Art itself is Dark Is Not Evil, but the negative cultural associations make the establishment distrust it.
 * Can empower normal people to stand up to it. Expect the Establishment to be a Hypocrite that wields these arts in secret to oppress the people.
 * Could change the status quo by altering social, economic or military realities. This can be good if it would remove the weakness in a Terminally Dependent Society (and bring the corrupt leaders down with it), or bad if the change would cause widespread chaos.

There are a lot of possible tropes that can be treated as a Dark Art, here are a few:
 * Black Magic
 * Blood Magic
 * Creating Life
 * Dangerous Forbidden Technique
 * Anything when it's done For Science!,
 * Resurrection
 * Everything in the Scale of Scientific Sins
 * Touch of Death
 * Robotics and AI research
 * Politics

So, just who practices the Dark Arts in spite of all these dangers? Lots of people/things, actually. If it's magical, then an Evil Sorcerer, if it's a science then a Mad Scientist of course, and if it's a martial art then the Arrogant Kung Fu Guy is likely to know it. Expect them to learn their craft in the Academy of Evil. Even though the only crime in art is bad taste, the Mad Artist usually knows how to drive viewers mad (in the bad way) with their art. A hero might be able to "redeem" the Dark Arts, or at least use them without becoming damned/addicted when the Godzilla Threshold is crossed.

Anime & Manga

 * Magia Erebea in Mahou Sensei Negima. Or maybe that just is the Dangerous Forbidden Technique.
 * This will probably depend on how long the series lasts, and if the story line rejoins the "real" world long enough before the end for the author to want another round of upgrades for the cast. If so, it'll probably turn out the technique in question is a crude first step in Magia Erebea the real Evangeline moved beyond centuries ago. If not, it'll probably get dumped for a completely different technique of awesomeness.
 * Not dropped, Negi isn't even  anymore due to overuse of Magia Erebea. Of course, that just seems to mean he has it on permanantly.
 * Human transmutation from Fullmetal Alchemist.
 * The magic-users of Rental Magica has the set of taboo, mainly prohibiting things that either turn the user into an insane Blob Monster more often than not (including resurrection) or cause a massive area contamination. A plain magical crime (like slaughtering the whole village to get a lot of zombies quickly) apparently isn't lumped with it. Of course, there's an opposition, Ophites.
 * In Naruto, Forbidden Jutsu are any jutsu that are either too dangerous (e.g. FRS, which nearly destroys Naruto's arm) to perform, or plain immoral (e.g. Edo Tensei, which involves human sacrifices), preferably some combination of the two. Bear in mind that normal jutsu include mind attacking illusions, fireballs and lightning attacks used for assassination, any of which can kill the user if used too much. That's an idea of how bad these can be.
 * The Cybderdarks in Yu-Gi-Oh! GX. Apparently the wrong set of children's playing cards exude evil energy and can give people heart attacks.

Literature

 * Comes up in Harry Potter, obviously, though not very well-defined, and it's never explained why some spells are Dark whereas choking someone on soapsuds or setting people on fire aren't.
 * Though stereotypically, it basically still makes Necromancy the definition of the Dark Arts. Or things resembling Necromancy evil.
 * It's notable that there's some categorisation in-universe on the seriousness of offensive magic, as such spells are called either jinxes, hexes or curses. Jinxes are defined by Word of God as "spells whose effects are irritating but amusing". Hexes are darker, intended to cause some pain or discomfort, while curses are described as "the worst kinds of dark magic".
 * Actually, the spell about the soap wasn't Dark Magic. The spell in question, Scourgify, is a cleaning spell, but a cleaning spell that was being used negatively. Likewise, the setting someone ablaze spell was most likely Incendio, which is more commonly used for lighting fireplaces. Spells that were created for the specific purpose of causing harm to any human being are Dark Magic. Hexes seem to be interchangeable with jinxes for the most part, though. Some spells are misnomers, as well, simply because of the Rule of Cool. The Bat Bogey Hex's effects sound like it'd be more of a jinx, but "Bat Bogey Jinx" simply doesn't have the same ring to it. You can't simply go by Charm/Jinx/Hex/Curse. "Curse of the Bogies" sounds like it's more of a jinx. It sounds like it just produces excessive bogies. Again, Jinx doesn't add to the name. Jinxes and Hexes are usually just playful tricks, and are mostly synonymous. Some spells are called what they are for the sake of Added Alliterative Appeal, like the Hurling Hex, which sounds more like a curse. Knee Reversal hexes sound like they'd be more like a Jinx, albeit a suffering one.
 * Quoth Professor Binns in explaining the Chamber of Secrets to the class, he points out: "Just because a wizard doesn't use Dark Magic doesn't mean he can't." And most of the really Dark Arts in Harry Potter do require the practitioner to do something morally compromising to perform - the Unforgivable Curses require the caster to feel malice, the Resurrection potion requires grave-robbing, mutilation, and torture of ones enemies. Recreating a body requires acts so horrific they made Rowling's publisher vomit afterwards, and making Horcruxes requires murder, in addition to other as yet unspecified unpleasantness.
 * Blood magic in Trudi Canavan's The Black Magician Trilogy.
 * Randall Garrett's Lord Darcy series. A royal investigator in a magical world.
 * "Black magic is a matter of symbolism and intent."
 * "Black" magic uses dark symbols and/or intends to harm. It inevitably harms the soul of the practitioner.
 * In one story, a major MacGuffin is a magical device that disrupts those intending to do harm. Since it only sows confusion instead of intending harm it is not itself black magic.
 * Necromancy is the most common Dark Art of fantasy, occuring at almost any setting where magic exists.
 * The Dresden Files has the Seven Laws of Magic laid down by the White Council that bar against certain types of magic; the penalty for breaking any of them is death. These laws prohibit: using magic to kill a mortal, Necromancy (specifically, human necromancy), Time Travel, changing another's shape, Mind Rape, enthrallment of another, or summoning Outsiders.
 * Note that Mind Reading is considered to be Mind Rape, when done through human wizardry, and any kind of death spell (as opposed to lethal combat magic) is The Dark Arts regardless of its target. The Laws are written to be easy to enforce.
 * Over the course of the series, the perspective presented on these has expanded from "even accidentally infringing on the Laws will irrevocably twist you into a two-dimensional villain who needs to be put down" to "okay, so there are a few people who break the Laws and stay sane, which means finding and killing them early on is even more important". A reasonable (if disappointing) attitude for a governing body to take, especially one which explicitly states its laws are not intended to reflect any society's conception of morality or justice.
 * In Dragaera normal sorcery is done by manipulating the energy of raw chaos which has been filtered through the Imperial Orb. Elder sorcery is done by directly manipulating raw chaos, and by imperial edict practicing it carries the death penalty, because making a blunder with raw chaos... well, the results would be Bad with a capital B. Of course, this doesn't prevent several of the main characters from dabbling in elder sorcery.

Tabletop RPG
"Duke Justinian: Hodar, you dared to defy a royal order and continued to dabble in sorceries which I had forbidden to all the people of my realm."
 * Dungeons and Dragons adventure C2 The Ghost Tower of Inverness.


 * Later editions has a wide range of spells tagged [evil]. Many are poorly explained (Animate Dead uses raw energy to create a non-sapient construct, while golems, which involve enslaving a sapient being, have no such tag) have it for no reason whatsoever (such as Deathwatch, which basically says if a person is dead, near dead or alive). Later source books state that undead exude negative energy, and so make the world a worse place just by existing. That's just one spell though.
 * The Book of Vile Darkness sourcebook notes that any spell that taps into negative energy is dabbling in forces that are best left undabbled-with. To see someone's condition with Deathwatch, you're looking through negative-colored glasses. Animating a golem isn't truly "slavery", it's temporary (albeit long-term) attachment of a spirit to the parts (and in the case of clay and flesh golems, it's unstable attachment at that); it's arguable if they're even sentient. Raising a corpse as an undead, on the other hand, is the sort of thing that kills the grass on your lawn even if you're in the basement at the time.
 * In Forgotten Realms there are prohibitions from the gods of magic (covering Fantastic Nuke, endangering of the world's magical circuit and a few crimes against the magic-using community) plus whatever local laws and traditions don't approve, typically including the most unpleasant forms of necromancy and/or using wild magic in populated areas. From what is known about the elven kingdom of Cormanthyr, it prohibited some enchantments that allow massive binding of magical items and creatures, some blood magics, using mass-destruction and later also selective spells in modes aimed to harm elves or "allied" beings. A few areas don't approve arcane magic at all, claiming it's "dishonorable", but in fact it's the places when magic may attract a curious spell-grub, and no one wants that anywhere around.
 * Dark Sun defilers aren't tolerated by anyone including most other defilers, and all magic is looked upon with at least some suspicion because of this.
 * In 4th Edition, the Warlock and classes with the Shadow power source are this.
 * Champions supplement The Blood and Dr. McQuark. People on the planet Ea are forbidden to use magic or powers that involve interdimensional travel because it could lead to the unleashing of Eldritch Abominations.
 * Blood magic and Toxic/Insect shamans in Shadowrun.
 * The World of Darkness settings (Old and New), naturally, are full of those.
 * Infernalism all round the oWoD: Nephandi, Baali, Black Spiral Dancers, Earthbound Thralls...
 * Left-handed Legacies for the Mages of Awakening.
 * Refinement of Flux for the Prometheans.

Video Games

 * Any magic in Vagrant Story, explicitly so.
 * Dragon Age has Blood Magic. While magic itself is not evil, blood magic revolves around using life force for power. Most of the blood mages in the game are evil, or at the very least enemies of the heroes. The power is also taught to humanity by personifications of emotions (ingame only a personification of desire teaches it, no information on which emotions are able to), and while it can just be used as an alternate means of powering normal spells, the big headline blood magic spells allow for Mind Control, blood-boiling and similar nastiness. Also, of course, the life force you use to power the spells need not be your own, a temptation that few blood mages can resist.
 * Although other magic schools serve to light people on fire or freeze them alive, hurt or even kill them by tormenting them with visions and so on.
 * According to one codex entry, the Tevinter archons of old were taught Blood Magic by the Old God Dumat the Dragon of Silence. Since an Old God is basically an Eldritch Abomination that happens to look like a dragon this makes Blood Magic even more unsettling.

Western Animation

 * Avatar: The Last Airbender has Bloodbending which lets user control water in a body of another person turning him/her into a Human Puppet. This technique is mostly seen as morally questionable, because it takes away victim’s freedom and violates his/her body. There are also other – more terrifying – implications, but they are never brought up, because its kids show. Almost every known Bloodbender seems to use it for sinister purposes (Hama kidnaps innocent villagers,  forces Korra out of the city) and only one that doesn’t (Katara) has to be forced to learn it, because she is terrified and disgusted at a very thought of using it on another human being.

Real Life

 * Supposedly, to this day no respectable medical scientist admits using knowledge gained from Mengele's archives.
 * Then again, Mengele was such a bad scientist that there is nothing to glean from his files.
 * On the other hand, the experiments performed by the Japanese Unit 731 were just as bad, if not worse, than the experiments of Mengele... Except that the people who performed them got away with it, because the U.S. government offered them amnesty in exchange for their research. Some of them are still alive and still claim that vivisecting human beings without anesthesia was a perfectly sensible and moral thing to do.
 * A lot of what humans know about the effects of freezing and phosgene gas on the human body comes from Nazi experimentation - the ethical debates are still raging.
 * Improvised Explosives. While modern technology makes it impossible to completely eradicate such knowledge, the authorities become VERY unhappy if they find out you know this stuff.
 * In Less Wrong parlance, this is used to refer to the use of faulty logic, fallacies and self-deception, Double-Speak... in two words: Bad Faith. Even for ultimately good purposes, those arts are a double-edged sword. Truth, and logic, ultimately, always win.
 * Despite only making the headlines in mid-2011 with the News of the World Hacking Scandal, journalists have for a long time referred to the use of telephone and email hacking as "The Dark Arts". Apparently it used to be common practice BUT IS DEFINITELY NOT ANYMORE.
 * Of course then there is cult-esque brainwashing and other psychological manipulations/abuse. You may get a laugh or two if you mention being curious about them though.
 * Some people hold an ostensibly Christian belief that even pretending to use magic in, say, a computer game is bad, even though such games are usually set in a fictional universe where the fictional magic is known to not actually be from the devil even in-universe.
 * The third type is a common theme in weapon bans. Bans on switchblades, saps, and "Saturday Night Specials" were billed as ways of keeping weapons out of the hands of "those sort" of people. While a ban might include your Perazzi shotgun that costs as much as your SUV, it was billed as going after the riot shotguns that the inner city badguys were shown using in that movie. Likewise, bans on bearing arms were rather selectively enforced, and "may issue" concealed carry permit laws allowed similar discrimination.