Despite Harry Potter using Unforgivable Curses, one of the Unforgivable Curses Harry Potter never used the Killing Curse for several reasons. Avada Kedavra was Lord Voldemort's signature spell.
The darkest of the Dark Arts, Harry Potter unforgivable curses are the Cruciatus Curse, the Imperius Curse, and the Killing Curse. Although the curses are highly illegal, Harry using Unforgivable Curses happened, but he uses them once he was thrust into the Second Wizarding War.
Harry Potter is the only known person to have ever survived the killing curse in the franchise, and twice.
The disarming spell would have specifically taken away Voldemort's powerful wand. Even if he were to use a Death Eater's wand after that, it wouldn't be the Elder Wand. Also, the time between disarming & rearming Voldemort could be used to decisively defeat Voldemort.
No, harry did not use the killing curse at all (he used the expelliarmus spell in the picture above). Voldemort's own killing curse rebounded on himself when Voldermort's wand (aka the Elder wand) realised that Harry is the true master of it.
During his final confrontation with Voldemort, Harry knew that he (Harry) was the Elder Wand's true master. He again cast Expelliarmus, ejecting the wand from Voldemort's hand into his own as the Killing Curse rebounded off his body, fatally striking Voldemort.
Speak to Sebastian in the Undercroft after this and he'll teach you any Unforgivable Curses you have missed up to that point, including Avada Kedavra. It's worth learning the curse as doing so should have no negative outcome on the game's story.
In order to conjure the avada kedavra curse, you have to want to kill your victim. We all know that Voldemort could easily kill a child without an ounce of remorse... but not Snape. Snape didn't want to kill Dumbledore, and this was why the spell was blue instead of the usual green.
Her sacrifice gave Harry the power of love, a protection spell sealed with the blood spilled by her death.
Defeating The Dark Lord with his signature spell
Disarming is about defence, not murder. Voldemort was a killer, Harry was not. It was an important distinction for Harry, who had learned so much about Voldemort and seen first-hand the ways in which they were similar.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
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.
The reason it is described as unblockable is that the use of the shield charm is ineffective against a killing curse, as explained by fake Alastor Moody in Goblet of Fire. You can, however, protect yourself by summoning physical shields like Dumbledore did in the Battle of the Ministry of Magic.
And the third, the Killing Curse, is named by Hermione; Moody mentions that it can't be blocked, and only one person is known to have ever survived it: Harry Potter. Harry makes use of two of the Unforgivable Curses in the books.
The Killing Curse ('Avada Kedavra')
Obviously there's no coming back from this spell, and according to the Ministry of Magic's classifications (and, again, fake-Moody) this is the worst Unforgivable Curse.
They are the Killing Curse, Avada Kedavra, the Cruciatus Curse, Crucio, and the Imperius Curse, Imperio.
Sectumsempra is a curse invented by Professor Severus Snape, during his childhood, when he was known as "The Half-Blood Prince". He created it with the intention of using it against his enemies, and it soon became one of his specialties.
James's Animagus form was that of a stag, which earned him his nickname, Prongs. Strikingly, Harry's Patronus was a stag and his mother Lily's was a doe, a female deer, showing that the family's characters were in harmony and formed part of the same animal group.
Sybill Trelawney
James and Lily were in the original Order of the Phoenix and therefore knew they were risking their lives in the war against Voldemort. Still, the Dark Lord's whole reason for trying to kill them all was to eliminate the threat posed by a certain prophecy.
He truly believed the Elder Wand had to be passed down through murder, because that is what the legends say. But even if he knew that one only had to be disarmed, Voldemort was still too arrogant to do that. He kills anyone in his way.
Quirrell didn't use the Killing Curse on Harry, because Voldemort said “use the boy” to get the Sorcerer's stone from the Mirror of Erised. If Quirrell had killed Harry right away, he would have lost the chance to get the stone.
Its incantation is Avada Kedavra. The only known counter-spell is sacrificial protection, which uses the magic of love.
Unfortunately, while you'll be able to use it in the arena, you won't have access to it anywhere else. So if you are looking for another chance to learn Avada Kedavra in Hogwarts Legacy, you can't really, but you can use it for a while at the Dark Arts Battle Arena.
In case you do turn Sebastian in, he will be taken away by the Ministry authroities, and you won't be able to learn Avada Kedavra. This way, Hogwarts Legacy has multiple endings.