Entropy and Chaos Magic

In fiction, entropic magic often represents chaotic or highly destructive magic, almost always used by the demons or other evil forces in the world.

Chaos magic often fills one of two flavors:

1. Magic based on randomness. Use of this magic will often cause unpredictable effects, or will cause effects based on wild, uncontrolled energies.

2. A form of magic the same as, or closely associated with, entropy magic as described above.

Might be related to Antimatter and Casting a Shadow.

Literature

 * The Lone Power in the Young Wizards series has the main goal of bringing death to the multiverse by spreading entropy everywhere (he's also responsible for the creation of entropy, by the way), and his powers are magical in nature. Conversely, the proper application of magic can slow entropic decay.
 * In the Saga of Recluce pure Chaos is basically pure energy, but it has entropic side effects. Chaos mages age faster than normal humans, the wine they drink turns to vinegar before they're finished with it (or even after a minute or two for very powerful mages), books they read fall apart after a few years, and the city where the chaos mage guild is located is covered in a thin layer of fine white dust formed from Chaos energy slowly destroying the stones of the city.
 * In the Chalion series, the demons bound by sorcerers are innate creatures of chaos. One way to keep a demon tame and easier to control is to 'shed' entropy, by causing little forms of decay, rust, or rot. (In one case, a sorceress caused milk to sour and wine or beer to go bad, at this one particular inn, in order to keep her demon occupied. Another powerful but poorly-trained sorceress used the entropic powers to aid in laying siege to a fortress, destroying stored food, potable water, and many of the weapons.) Inversely, using sorcerous magic to undo some form of destruction is 'extremely difficult, but possible. (A sorcerer mentioned having reconstructed a burnt letter, at great cost.)
 * In a variation, Aornis Hades in the Thursday Next series manipulates entropy to affect chance. Specifically, by lowering entropy in order to cause improbable and fatal accidents. This has the side-effect of causing numerous, unrelated coincidences to pile up just prior to the accident--long enough for Thursday to realize the attack is coming.
 * The initial impetus for the main plot of the sixth The Dresden Files book is when Harry is hired to deal with an entropy curse that kills its targets in strange and unusual ways. A previous victim is killed after being hit by a car... while water-skiing. Harry manages to intercept and redirect another use of it that causes a frozen turkey to fall out of a passing aircraft and pulverise an attacking Black Court vampire and just for extra value, cause the cooking timer to pop out and ding.

Tabletop Games

 * Red magic in Magic the Gathering. It's allies colours Black and Green sometimes show aspects of this.
 * Dungeons and Dragons
 * There was at least one prestige class in 3.5 DnD called the "entropmancer" who used a "shard of entropy" as its main weapon. They kinda screwed up the whole physics thing there, but the thematic link is obvious.
 * The 2nd Edition supplement Tome of Magic had Wild mages and the Chaos sphere for priests. Both emphasized chaotic spells with random results.
 * After the Time of Troubles the Forgotten Realms developed Wild Magic Zones, where any magic use could cause a random Wild Magic Surge which was often quite dangerous.
 * The Wand of Wonder (several varieties), which had a different effect each time it was used.
 * In 4th Edition, Sorcerers can choose Wild Magic as a spell source, which is described as channeling power from the Elemental Chaos. To go along with the theme, many Wild Magic powers daze or stun enemies or have an effect determined randomly via die roll. Even boons from various Wild Magic features are determined randomly.
 * The Euthanatos in Mage: The Ascension are masters of the Sphere of Entropy. In broad strokes this means they can tell when things are going to break down and they can make things break down.

Live Action TV

 * Buffy the Vampire Slayer had Ethan Rayne, who worshiped chaos and often used chaos magic.

Video Games

 * War Craft: Several names of demons are based on the word Entropy. Demons in warcraft 3 use chaos magic, and also have a number of "chaos" spells.
 * Chaos Knight from DotA uses this.
 * Fall From Heaven
 * The entropy magic sphere is associated with the most the main evil god, and its spells relate to decay and corrosion. Entropy magic nodes act as a source of Hell Terrain, and any mage who uses the magic will come back to life as a slave of the Legions of Hell upon death.
 * The chaos magic sphere is a flavor 1 chaos type, and is associated with the god of war (in a Anarchistic, everyone fights everyone, sense.), who is a fallen, evil god as well.
 * Lords of Magic's chaos faith uses flavor 1 spells.
 * Heroes of Might and Magic IV has a spell school literally called Chaos Magic, and consists mostly of direct damage spells. Heroes of Might and Magic V has an entire school devoted to destructive spells, as well.
 * Dungeon Crawl has Annihilations. Exactly What It Says On the Tin.
 * ADOM features a variety of magicians devoted to Chaos, including the Chaos Archmage, guardian of the elemental Mana Temple. His powers are no more random than those of any spellcasting enemy, but he's much meaner than most of them. Like most of the other Chaos-themed creatures in the game, he can also corrupt your character with a melee touch attack, which produces a series of randomized warping effects.
 * Entropy magic in the Dragon Age series is mostly consisting of curses and other sinister powers, and closely connected to The Fade.
 * The Bonus Boss and True Final Boss of The Reconstruction have "Chaos" as their element, as opposed to a certain optional character with "Order" as his element. Both end up effectively Non-Elemental.
 * Entropy is an element in, well, Elements.
 * In Dungeon Siege III, this is used by Reinhart though the spells are more like Formulaic Magic that focus on DPS.

Webcomics

 * "Entropic Acid" is used to destroy a Nigh Invulnerable parasite in The Dragon Doctors. There's also been mention of an "Entropic Zone," a dimension where life forms age and objects decay at an accelerated rate.