Notes

Dark Arts : any magic used to cause harm (spells, potions, dark creatures)
The use of dark magic corrupts (like Voldemort) and rips soul apart.

No law forbids the practice of dark magic, except for the Unforgivable Curses (-> Azkaban).
Aurors use it to fight their enemies.

Jinx : lowest form of dark spell, often used as a practical joke, not an inconvenience. Anti-Jinx to prevent the use of a Jinx, Counter-Jinx to remove a Jinx.
Hex : slightly darker, moderate discomfort, major inconvenience. Reversed with a Hex-Breaker.
Curses : darkest, most extreme dark spells, long lasting, extreme discomfort, pain, death. Blocked by protective charms, lifted by counter-curse.

Knockback Jinx (Flipendo, "Fli-PEN-Doh") :  repels or pushes back the target with a blue light. Could blast a fragile target. Can be sent back with Disarming Charm or Shield Charm. Wand movement : slash down, to the right, up diagonally to the right, a wave.
Knockback Jinx Duo (Flipendo Duo) : more powerful, shower of blue sparks. Multiple castings in a row can cause small whirlwind. Wand movement : slash.
Bat-Bogey Hex : bogeys turn into bats and fly out of the target’s nose
Curse of the Bogeys (Mucus ad Nauseam, "Mew-Kus AD Naw-See-Em") : target develops an extreme cold and an extremely runny nose. Could cause collapse. Draw raindrop in front of you.

Essay

Prompt
Write on your opinion of the legal status regarding the Dark Arts. Should they stay legal or should it be a crime to use them? Why or why not?

Response
I think the practice of Dark Arts should be more regulated by law. The Ministry of Magic should set more limits regarding the use of Dark spells, particularly the curses. Jinxes should not be concerned, since they don't cause real harm. The use of hexes should not be punished neither, except maybe if a person uses it on a regular basis. The use of curses should only be allowed in a context of defense, for example if you're attacked by a dark wizard. People that use curses should be punished, even slightly, to prevent them from doing it again. For example, you could seize their wand for a limited period. 

The punishment must not be to severe: people that used a curse once should not be put into the Azkaban Prison, but be educated to avoid recidivism. This system would be there to protect people, not to make them afraid of going to prison if they use the wrong spell.

A problem that could appear is that the fact that Dark Arts are more regulated could incite some people to practice them, just for the thrill of illegality. I hope that wizards would know that using magic to harm people will also harm them by corrupting them.