Dark Arts (Earth-1107)

"The Dark Side of the Force is a pathway to many abilities some consider to be unnatural..."

- - Chancellor Tywin Lannister to Galen Marek

The Dark Arts are aspects of the Force mainly used to cause harm, control, addiction, and even death of others and its user. Those who resorted in Dark Arts developed their power from emotions such as fear, anger, hatred, obsession, and violence. The Sith are the practitioners of the Dark Arts, and are the mortal enemies of the Jedi. The Dark Arts encompasses many abilities and actions from Unforgivable Curses to alchemy, and its practice is illegal.

Nature of the Dark Side
"I have experimented; I have pushed the boundaries of the Force further, perhaps, than they have ever been pushed — Of some kinds. Of some. Of others, woefully ignorant you remain. The old argument. But nothing I have seen in Nirn has supported your famous pronouncements that love is more powerful than my kind of Force art, Yoda."

- - Darth Tyrannus and Yoda

The Dark Arts are aspects of the Force, a metaphysical power that bound Nirn together. The Dark Arts are generally regarded as corrupting to those who use them (which is part of the reason it is considered "dark"). After engaging in them extensively for many years, many start to degenerate and lost their former appearance.

Master of the Jedi Order Yoda, in particular, suggested that engaging in any shape or form into the Dark Arts that involve murder is damaging to the soul; for instance, Obi-Wan Kenobi attempted to convince himself that in the aftermath of Order 66, the soul of his apprentice, Galen Marek, was "not yet so damaged" that he is probably capable of murder, but that he already went with cold blooded murder, stating his soul would be "ripped apart" and "far too gone".

As studied by Jedi scholars, it is indeed proved that manipulating the Dark Arts radically, such as Avada Kedrava, the Killing Force power, damages an individual's soul. The dark art of creating a Horcrux involves literally splitting the soul for the unnatural purpose of achieving immortality, an art learned by Darth Plagueis and passed to his apprentice Darth Sidious. Darth Tyrannus was interested in the Dark Arts, initially by a theoretical view, but his curiosity turned to avarice, and eventually he was completely drawn in and corrupted.

According to Darth Sidious, the Dark Arts are pragmatic in nature, where every time a branch is defeated, it only comes back "fiercer and cleverer" than before. It is therefore imperative that one's defenses must be as versatile as these foul arts themselves. Darth Sidious believed that the source of the Dark Side was the universe beyond the edges of Nirn.

Powerful Dark Arts also require malicious intent in order to be successful. To cast Cruciatus, for instance, one must truly desire to cause pain in and of itself, according to Darth Usir. The Dark Arts are also be difficult to control; injuries caused by the Dark Arts sometimes never fully heal, such as Darth Sidious's face after it was electrocuted by his own Avada Kedrava, deflected by Mace Windu.

If the presence of the Dark Arts is significantly powerful, nearby Force-sensitives could feel cold, such as when Darth Usir was near Chirrut Îmwe and Obi-Wan Kenobi, or when Jyn Erso sensed the Dark Side emanating from the Dark Cave on Dagobah.

Ethical Considerations
While the Dark Arts have a bad reputation, overall, they are not, by definition, "evil". Indeed, the Dark Arts can be used for good as well as evil. At the same time, the Dark Arts' abilities are not the only types of Force powers that can be used with the intent to kill.

The only exception to this rule is the spell which creates a Horcrux; an entirely selfish act — taking a life in order to prolong one's own. This act is so reprehensible that the caster's soul becomes fragmented, allowing the creation of a Horcrux. The soul can only be restored by complete remorse for the murder, or repentance, which is actually painful enough to cause death.

Source

 * [1], [2]