You’ll get it basically at the end of the game
Avada Kedavra, otherwise known as the unforgivable “killing curse,” is actually in Hogwarts Legacy as a playable spell. Not only do you get it temporarily whenever you’re playing through the Dark Arts battle arena: you can also earn it permanently at the end of the game. Here’s how to learn it.
Avada Kedavra is unlocked through a late game sidequest in the Sebastian storyline
Players will unlock Avada Kedavra through the quest In the Shadow of the Relic, which is an endgame level 28 quest. That’s actually a higher level requirement than the main storyline, so odds are you’ll be seeing it at the conclusion of the story, or in the postgame. Note that you need to finish the Sebastian side questline up to this point, so clear out all of the “In the Shadow of…” selections in your quest tab.
Once you do get the questline, it’s extremely straightforward. Go to the tomb with the quest marker, and enter it. Walk to the end (past the main altar door) and open up the crypt shelves, layering the piles of bones to create a bridge. You’ll encounter Sebastian, and engage in a spoilery boss fight. After the fight is finished, Sebastian will vaguely talk about the Avada Kedavra killing curse. If you wish to learn it, tell him that more people could stand to know the curse, and say “yes” when he offers to teach it to you.
Avada Kedavra is held to a long cooldown period (the time in which you can cast it again), but it’s extremely powerful, and will even one-shot elite enemies like armored trolls. You will get to use it for the rest of the save file, and that includes all the arenas you want to farm for XP, all of the remaining quests you have, and any open world activities.
There are no in-game morality issues with using it, even directly in front of friendly NPCs (professors and students alike) during combat.
