Nagini, Voldemort's snake, then eats Professor Burbage's dead body. A story about her "resignation" from Hogwarts appears in the Prophet, but members of the Order of the Phoenix discount it, as they are unable to locate her anywhere after that.
Nagini assisted with many of Lord Voldemort's murders
While Arthur lived to tell the tale, others were not so lucky. Lord Voldemort callously fed Muggle Studies teacher Charity Burbage to Nagini after performing the Killing Curse.
Nonetheless, despite her initially benevolent nature, Nagini's blood curse eventually turned her into a snake permanently. Though it is unknown if she became evil as a result of that, or was turned evil as a result of Voldemort turning her into a Horcrux. As a snake, Nagini was completely loyal to Lord Voldemort.
Charity Burbage floats helplessly above a dinner table, as if paralysed. She begs Snape to help her. Voldemort point his wand at her, and a green light erupts out of its end. The light hits Charity, and she falls down on to the table dead, her eyes open and her face splattered with droplets of blood.
Harry Potter and the Deathly Hallows: Part 1 Burbage pleads Severus Snape to save her, moments before her murder. During their stay at Hogwarts, Charity was friends with fellow Professor Severus Snape.
Nagini, Voldemort's snake, then eats Professor Burbage's dead body. A story about her "resignation" from Hogwarts appears in the Prophet, but members of the Order of the Phoenix discount it, as they are unable to locate her anywhere after that. Burbage is later replaced as Muggle Studies teacher by Alecto Carrow.
Although Snape may not have projected his memory of James onto Harry, he still would have been predisposed to dislike him by virtue of him being James Potter's son. Harry being in Slytherin would not have changed this fact.
Myrtle Warren was once a Hogwarts student, but after her untimely death, she stayed back as a spirit to eternally haunt the second-floor girls' bathroom. Myrtle had a hard time at Hogwarts, and was frequently bullied. Prone to wailing morosely, the ghost became known informally as Moaning Myrtle.
Bathilda is a very old witch and the former neighbor of the Dumbledore family in Godric's Hollow. As such, she knows quite a bit about the family's past, including the darker and more tragic parts. As the great aunt of Gellert Grindelwald, it was actually Bathilda who introduced Dumbledore to the future Dark wizard.
Isaacs brings up Lucius' disheveled appearance in Deathly Hallows, raising the possibility that the Malfoy patriarch had begun drinking too much. The way Isaacs saw it, Lucius was in a no-win situation. Given everything he'd done, the man no longer had a place on either side of the war.
Voldemort had a special relationship with Nagini, as she was his pet and one of his Horcruxes. According to Dumbledore, Voldemort had strong feelings for Nagini that he had not for anyone else; she was the one living thing that he had ever cared about.
When Harry and Hermione are on the first floor of Bathilda's house, Nagini (inside the corpse of Bathilda) tells Harry to "Come!" from the next room in Parseltongue. In reaction, Hermione jumps and clutches Harry's arm, and the two of them obey the command.
Unless one or the other has a significantly smaller role in the films than we are led to believe, Dumbledore and Nagini will get to know each other. From the very little we see of Nagini, it looks like she's at least potentially on the same side as Dumbledore.
There's been speculation he may have found her while in exile in Albania between 1981 and 1994, where he assumed a phantom-like form and possessed many animals (however, only snakes could bear him inhabiting their body). This could have something to do with his propensity to speak Parseltongue.
Harry quickly tells Neville that he must destroy Nagini, Voldemort's snake. Nagini is the last Horcrux that Voldemort created and the last one to be destroyed. During the final battle of Hogwarts, Neville pulls the sword of Godric Gryffindor from the Sorting Hat and beheads Nagini, destroying the last Horcrux.
Though it may later be revealed that the Dark Lord did indeed know that Nagini was a Maledictus, there's currently no indication that he (or anyone else) ever thought that she was anything other than a snake who was made into one of the Dark Lord's Horcruxes.
Moreover all she could hear would be hissing from the other room which can easily be disregarded. That is why Bathilda didn't speak in the same room as Hermione otherwise she would have made the connection that the hissing sound is actually coming from Bathilda herself.
Bathilda Bagshot has actually been dead for weeks, which explains the flies and blood handprints Hermione finds. Her body has been inhabited by Nagini, Voldemort's snake put there to trap Harry because Voldemort suspected, just as Hermione said, that Harry would return to the town where he was born.
In Harry Potter and the Deathly Hallows, Voldemort thinks that killing Snape will give him full control of the Elder Wand. He uses his snake, Nagini, to kill Snape rather than any number of spells he knows. This allows Snape to live long enough to help Harry defeat him.
Moaning Myrtle
Born in the late 1920s to Muggle parents, Myrtle Warren started her Hogwarts life in the early 1940s, where she was sorted into Ravenclaw.
Unfortunately, that man was the Bloody Baron, who was head over heels with Helena, and stabbed her in a rage when she refused to come home. After Helena was tragically killed, legend tells us that Rowena Ravenclaw died of a broken heart.
Moaning Myrtle is a ghost of a female student that can be found crying in girls' lavatories. She belongs to Ravenclaw and was killed by Basilisk for being a Muggle-born witch.
Horace Slughorn (1997 - present) Horace, after being convinced by Dumbledore and Harry Potter, returned to Hogwarts as the Potions master. After Severus killed Dumbledore and became headmaster of Hogwarts, it was decided that Horace was to become the Head of Slytherin House once again.
He even sent his Patronus to guide Harry Potter to the sword of Gryffindor (a known Horcrux-killer) in a nearby lake. Months later, Potter returned to Hogwarts for one final battle between good and evil, between the students and teachers of Hogwarts and the dark forces of Lord Voldemort.