What Dark Magic was the young Severus Snape using?

Question

I've read in a number of places about how Snape was already interested in dark magic when he was young because he thought it would make him powerful. Apparently, he thought that his esoteric knowledge and the power it would bring him might even make him more attractive to Lily Evans.

It's unlikely he was using any unforgivable curses, so just what was he using that wasn't unforgivable? What kind of spells could he have been experimenting with or studying that would not have gotten him in trouble?

Answer 1

In Harry Potter and the Half-Blood Prince, we have one canonical example of a spell that is absolutely within the realm of dark magic, created by Severus Snape: Sectum Sempra. In his old potions book, it showed several variations scratched out, and the final version.

Later, when Harry tried to use it against him, Snape said:

"You dare use my own spells against me, Potter? It was I who invented them — I, the Half-Blood Prince! And you'd turn my inventions on me, like your filthy father, would you? I don't think so… no!" - indicating that he created the curse.

There were likely more, given Snape's intelligence, but from the books, this is the only confirmed spell that he took credit for.

Levicorpus also appears to have been invented by Snape, according to some sources. The quote above seems to indivate that this is the case, as James had used Levicorpus against Snape as well. I don't know if it's evil enough to be considered "dark magic", however.

The Harry Potter Wiki has a few more examples of spells that are possibly accredited to Snape, but again, I don't know that any of these qualify as "Dark Magic".

From that site:

At the age of eleven, he knew more curses and hexes than most of the seventh year students. He reportedly was friends with a gang of Slytherins who later became Death Eaters, including Avery and Mulciber. Severus was credited with creating a good number of popular spells like Levicorpus, Liberacorpus, Muffliato, and curses like Langlock, the Toenail Growth Hex, and his signature curse, Sectumsempra.

Answer 2

I guess that any kind of dark magic would have got him in trouble, though at different levels (from school detention to wizard prison).

Being so talented at potions, as Slughorn recognizes ("why, not even you, Severus!"), Snape might have experimenting with potions to deal with friends and foes. For example:

• Healing potions (for himself, after most encounters with Sirius/James).
• Potions to improve concentration during exams (for himself/friends).
• Love potions (for Lily, assuming he had a physical, adolescent interest first, before falling in love with her).
• Poisons (for foes).

Not all of these are necessarily dark, but some of them are certainly illegal. Even a simple potion for concentration might be considered cheating, just like a self-correcting quill. And a love potion is quite dangerous and can certainly be used for dubious objectives bordering on illegality (see: Merope Gaunt and/with Tom Riddle Sr.).

Now, poisons might have been some kind of a favorite hobby for him. He had the talent, the enemies and the intention, so here's where I guess he put more effort. In my opinion, he studied and developed dark magic for this purpose.

However, it is not clear whether he actually used it on somebody, just as it's unclear that he ever used Sectum Sempra, because there's not much information on how spells are created (I guess at least you need to practice on somebody else). James and Sirius were his karma, but he did enjoy the company of bullies and "evil" people (as Lily tells him), so he most certainly might have had enemies other than the Potter gang, and he must have tried these dark potions on them.

This is only a wild guess, but as he did invent Sectum Sempra as a teenager (and marked it as being "for enemies"), I think it's likely he tried some other stuff as well. He would have been only too happy to poison James Potter just before a Quidditch match so he would fall off his broom five minutes into the game.