Just go undercroft and speak to sebastian again, to learn Adava Kedavra. You could've selected the dialogue option that doesn't give you the spell. You need to simp hard to get it. U didn't simp him enough.
Avada Kedavra being the most powerful and dreadful of the 3 Unforgivable Curses, can be unlocked only very later on in the game. You need to complete the Quest Line of Sebastian Sallow, at the end of which, you'll be given the choice of wanting to learn the Killing Curse.
You'll learn Avada Kedavra during the quest “In the Shadow of the Relic” — Hogwarts Legacy suggests that you're level 28 before you start it. To get “In the Shadow of the Relic,” you must have already completed: The relationship quest “In the Shadow of Hope” The main story quest “Lodgok's Loyalty”
You can also learn it in the next Sallow relationship quest where you should tell Ominis Gaunt "We must not turn Sebastian in." 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.
If you agree, then you get the chance to learn Avada Kedavra immediately. If you tell him he went too far, he will walk away and the quest will end. If you do choose to call him out, worry not, you can still learn the spell by visiting him in the Undercroft later.
The only way to truly learn Avada Kedavra in Hogwarts Legacy requires you to pick it up from Sebastian Swallow, as well as follow a specific path to get here.
Its incantation is Avada Kedavra. The only known counter-spell is sacrificial protection, which uses the magic of love.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Voldemort's signature spell was Avada Kedavra. Harry's was Expelliarmus.
The only real downside to using Avada Kedavra in Hogwarts Legacy is that it makes no sense in relation to the game's protagonist. Based on the way the fifth-year character acts throughout the story, some unsavory actions and dialogue may start to seem over-the-top or out of place.
Who is immune to Avada Kedavra? Phoenixes were semi-protected from the Killing Curse, due to them being immortal. In 1996, Fawkes swallowed one intended for Albus Dumbledore, causing him to burst into flame and die instantly. However, he then was reborn from his ashes.
History Of Avada Kedavra
The Killing Curse was created in the early Middle Ages by Dark witches and wizards. Primarily, the curse was used to quickly slay opponents during a duel.
Because the killing curse can be blocked. In the books, Dumbledore blocks it... with Fawkes. Because when you intentionally kill someone, you destroy your own soul, then again Dumbledore is in King's Cross station just like fetus Voldemort, so maybe he's there because he actually did kill his sister.
Ominous refuses to cast the spell again and warns that whoever does use it will be forever scarred, worse than the person on the receiving end.
Harry wasn't arrested for the simple reason that the people he used it on, Bellatrix Lestrange, Severus Snape and Amycus Carrow were in no position to make a complaint. Bellatrix was an escapee from Azkaban Prison who had just committed a murder in the Ministry of Magic.
He didn't block it. He enchanted a statue to jump in the curses path to be hit instead of the curse hitting Dumbledore. There is no way to block the curse - otherwise countless people could have easily been saved. The Abada Kedavra has no counter, cannot be blocked and is irreversible.
Avada Kedavra
It's used to kill people, it's an Unforgivable Curse, and it was Voldemort's favourite, so it's going last.
Alohomora, which is a spell that unlocks objects (and it's also Hermine Granger's signature spell).
Her sacrifice gave Harry the power of love, a protection spell sealed with the blood spilled by her death.
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.
Firestorm. Firestorm was a spell that created a large ring of fire around the caster's wand. This spell is one of the last and most powerful spells that Albus Dumbledore cast using the elder wand before his death.
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.