Repeated use of the Cruciatus Curse is torture and Bellatrix Lestrange subjected the Longbottoms to such extremes of pain that it sent them insane.
The first time Harry cast Cruciatus was in Harry Potter and the Order of the Phoenix when Harry Potter uses Crucio on Bellatrix Lestrange after she killed Sirius Black in the Department of Mysteries.
Harry makes use of two of the Unforgivable Curses in the books. Dueling with Bellatrix Lestrange, he attempts the Cruciatus curse, with limited results; Bellatrix says that he has to really hate someone to make the Unforgivable Curses work properly, righteous indignation isn't enough.
We know that they did not use Avada Kedavra. Aveda Kedavra has one effect: it kills. Other curses can be just as lethal.
The primary reason the Cruciatus Curse didn't work on Harry was that Voldemort wasn't the true owner of the Elder Wand. The Elder Wand, like other wands being semi-sentient, knew who it's true master was. It was aware of the fact that Harry had won over Draco and it belonged to him.
In Deathly Hallows, Hermione faced a real test of her physical and psychological stamina. After being on the run from a bunch of Snatchers, the gang were taken to Malfoy Manor, where Bellatrix proceeded to torture Hermione using the Cruciatus Curse.
There is likely a good reason that the Sectumsempra is not an unforgivable curse. It's mostly because Sectumsempra is Snape's personal curse that he created. It is not a widely known or used spell, and it is one that he kept secret — which means it can't be added to the list since no one really knows about it.
Cruciatus Curse ('Crucio')
Harry tried to use this spell himself. The first time was against Bellatrix after she had killed Sirius. His attempt was unsuccessful because, as Bellatrix mockingly explained: 'You need to really want to cause pain – to enjoy it – righteous anger won't hurt me for long…'
The clue he received in the film was from Bellatrix, who was in a frantic frenzy when she thought her vault was broken into. He is ultimately able to identify the cup as a Horcrux because of his ability to hear the piece of Voldemort's soul contained within them, an ability which is not present in the books.
Compatibility with Bellatrix's death: Bellatrix's sudden death aligns with the effects of the Avada Kedavra curse. Arguments for and against its use by Molly: Although Avada Kedavra is a possibility, Molly's character and values may make it less likely that she would resort to using an Unforgivable Curse.
Roughly translated, Expelliarmus – the Disarming Charm – means 'to drive out a weapon' and that's what it does: forces the subject to drop whatever they're holding. Usually that's a wand, which is why it's often seen in duels, and Harry definitely took that to heart, given how much he used it in combat.
The three Unforgivable Curses in Harry Potter are Crucio, Imperio, and Avada Kedavra, and all three are available to Hogwarts Legacy players. Crucio subjects the victim to extreme torture, while Imperio puts them under the control of the spellcaster.
Alohomora, which is a spell that unlocks objects (and it's also Hermine Granger's signature spell).
Malfoy spots Harry and casts a Cruciatus curse; Harry, defending himself, using the Half-Blood Prince's Sectumsempra spell without knowing its effects. To his horror, it gashes Draco's face and chest, spilling his blood everywhere.
His reaction to Bella's death was akin to his reaction at the loss of the Cup, which was when he realised that his own immortality was jeopardised amidst war and his own death could have been near.
Bellatrix Lestrange Killed her own cousin, Sirius Black: She killed Sirius (who was her cousin) during the battle at the Department of Mysteries. She was remorseless and was cackling in glee after she had murdered Sirius.
Draco's refusal to reveal Harry's identity to Bellatrix was not because he liked him. It was because he believed that Harry was the only chance they had at defeating Voldemort. At first, Draco admired and revered Voldemort until he threatened his family's safety.
He did not love anyone, and did not care to be loved. He felt nothing for his family, and only wanted his friends in school to rally around him because he wanted to hold power over them. Bellatrix Lestrange was obviously in love with him and worshiped him, but he only cared for her servitude, not her.
Harry knows from his conversations with Dumbledore that if a Horcrux is in the vault, it must either be the Hufflepuff cup or else an unknown object, so they have no choice but to look for the cup.
Lily was a muggleborn - to her, she was a mudblood. James married Lily and they had Harry, who is a half-blood. A pureblood is someone who has two pureblood parents. A muggleborn is someone with muggle parents, and a half-blood is someone with one pureblood parent and one muggleborn parent.
In the film Harry Potter and the Deathly Hallows: Part 2, this duel has some noticeable differences: In the film, Bellatrix casts a blue spell at Ginny Weasley instead of a Killing Curse, who deflects it using a Shield Charm.
Snape used this spell on George Weasley in Harry Potter and the Deathly Hallows, cursing his ear off. Mrs. Weasley remarks that as his ear was severed by Dark magic, it will be impossible to grow it back. Mentioning that it was Snape who did it, Lupin remarks that "Sectumsempra was always a speciality of Snape's."
Rictusempra, the Perpetual Tickling charm, which apparently can be stopped by the Finite Incantatem charm, was used by Harry against Malfoy in the Duelling Club. The intent was, of course, to tickle Malfoy to the point that he would be unable to jinx Harry in return.
But many people forget that he also invented a number of spells. In the Harry Potter movies, Snape came up with the Sectumsempra curse when he was a student at Hogwarts, and it's known to cause painful lacerations on the target. But the films don't explore all the spells Snape invented in depth.