Bellatrix boasts that she was taught magic personally by Voldemort. What do we think he taught her?

In terms of spell use, we largely see her use the same Unforgiveables as all the other Death Eaters. So it seems unlikely that he taught her spells designed for direct combat.

That seems to leave two main avenues:

- He practiced duelling with her and she learnt general duelling technique rather than specific spells.

- He taught her magic that is not directly applicable to duelling.

If the latter, we know she knows occlumency so maybe that is what he taught her. That would also involve him repeatedly using legilimency on her which may also be why he is so confident she is utterly loyal.

Otherwise, maybe some obscure dark magic that is more used outside of combat than in it? Things like how to raise an inferius.

 

Did Bellatrix have to know Occlumency to teach it to Draco? I always assumed she only knew Legilimency and used the Snape strategy of penetrating his mind over and over again until he was able to detach himself from thoughts/emotions. After all, Bellatrix doesn't exactly fit the 'profile' of an Occlumens – I can't really imagine her detaching herself in any manner. So maybe Voldemort taught her how to cast the Legilimens Spell and other esoteric bits of magic.

Although, if Bellatrix knew Legilimency well enough to use it on Draco, that begs the question why she didn't use it on the Longbottoms or Hermione. I guess the most likely answer is that she's just sadistic and/or too unskilled to interpret the response.

 

He might of taught her things like curse breaking to break into people homes. How to counter ministry spells, both offensive and defensive.

 

We could contest that statement instead.

What if she claimed that to emphasize her closeness with Voldemort rather than any magic? The Dark Lord did give everyone rewards and there must have been others who also wanted to learn from him.

We have Snape, who learnt the flight spell, and it was emphasized strongly in the books.

She does claim to know powerful spells, but we don't really see it or have it remarked on.

 

I imagine he taught her how he utilised negative emotion to power his spells. She was one of the last ones standing before she got beat by the power of Molly Weasley's love for her children.

Both their defeats were due to underestimating love, I imagine both their strengths came from the opposite.

 

I can imagine them duelling before Voldemort's first defeat, both as a way for Voldemort to keep his skills sharp, and so that Bellatrix and possibly other senior Death Eaters could learn through the experience, and be prepared for a possible confrontation with Dumbledore. Voldemort is also said to have widely travelled before he launched his terror campaign, searching out esoteric techniques and the like. I wouldn't be surprised if he had Bellatrix bring him anything interesting from the Black library/collections, sharing a little of what he learned abroad as a reward.

It's hard to tell for Occulumency/Legillimency. If Bellatrix was recruited straight out of Hogwarts, then he could have instructed her in both disciplines. Alternatively, they sound like the sort of thing a Black scion would have to learn from a young age.

Finally, she was trusted with one of his horcruxes. It seems probable that she would recognise it for what it was. He could have taught her how to make one, though that probably would be slightly ooc for him. Still, he does seem to have a special relationship with the Blacks, and trusted Bellatrix, Lucius Malfoy and Regulus with access to/the opportunity to gain knowledge about his horcruxes, so it's possibly he would have educated his right hand woman about the process. Whether or not she made one is up for debate. We don't know how common the practice was, but I suppose it was common enough for a book telling you how to do it to be sitting on a shelf in a school library. It would be in character for her to make one so that she could stay by his side forever. If he would give her permission to do so is another question.