There are three Unforgivable Curses you can learn in Hogwarts Legacy, each of them testing your morals more severely than the last. As you progress in your relationship with Sebastian Sallow, you will learn more about his past, and why he is so keen on walking this darker path.
Regardless of whether you agree with him or not, Sebastian will stop at nothing to cure his sister Anne from the curse that has caused her constant pain for years on end. Your journey together will take you into the depths of Salazar Slytherin’s Scriptorium, and the catacombs of Feldcroft. When the time comes, will you choose to learn the most formidable curse of all, Avada Kedavra? Here’s what you need to know in order to make that choice for yourself.
Quest Prerequisites
Before you can learn the most powerful spell in the game, you’ll have to progress through the majority of Sebastian’s story first. This includes learning both Crucio and Imperio, as well as completing a handful of additional quests with Sebastian.
After learning Imperio, you’ll need to complete In The Shadow Of The Mountain and In the Shadow Of Hope in order to progress Sebastian’s story. Unlike most of Sebastian's quests that proceed one after the other, you’ll unlock these last two simultaneously. In order to start these quests, you need to also learn Bombarda, so make sure to progress the Beasts Class questline. After learning Bombarda and completing both quests, you’ll finally unlock In The Shadow Of The Relic, where you’ll have the option to learn Avada Kedavra.
Into The Catacomb
Sebastian is recklessly pursuing the answers behind the artifact that can control dark magic in the hopes it will cure Anne. Before you arrive at the Feldcroft Catacomb, Sebastian has already headed inside. At the entrance of the catacomb, you’ll find Anne and Ominis sharing in their concern with Sebastian's actions, and their desire to stop him before he takes it any further.
After finishing the conversation, the three of you head into the catacomb after Sebastian. As you make your way further in, you learn that Sebastian has figured out how to control the Inferi inside the catacomb by using the artifact. You’ll need to defeat a couple of waves of them in order to reach Sebastian, so make sure you have Incendio and Confringo equipped.
After defeating them, Ominis will realize that Anne slipped away and is likely heading back to Feldcroft to get her uncle Solomon’s help. Last time you spoke with Solomon, he threatened that if Sebastian continued his pursuit of dark magic, he’d report him to the headmaster which would inevitably get him expelled. Ominis leaves to smooth things over while you head further into the catacomb to try to reason with Sebastian.
Confronting Sebastian
As you make your way further into the catacomb, you’ll enter a room with an exit just out of reach. Like your first visit to the catacomb, you’ll need to create a bridge by using the bones stored in the tombs. Start by casting Accio at the tombs on the walls to pull them open. The bones inside will fall to the ground, and you’ll cast Accio on them and bring them to the altar in front of you. After bringing both sets of bones, the bridge will be fully formed, allowing you to reach Sebastian in the following room.
You’ll find Sebastian surrounded by Inferi, only this time, they aren’t attacking him. The power of the relic really has given him control over them. As you try to reason with him, Solomon shows up and is mortified by what he finds. He quickly casts Accio at the relic, pulling it out of Sebastian’s hands, and destroys it. This releases the hold on the Inferi, and enrages Sebastian. As you and Sebastian fight off the Inferi, you will also be forced to cross wands with Solomon.
Learning Avada Kedavra
After defeating countless waves of Inferi and exchanging blow after blow with Solomon, the battle will finally end with Sebastian casting Avada Kedavra at Solomon in a fit of rage. Anne shows up just as Solomon falls lifelessly to the floor, and is mortified by the actions of her brother and the death of her uncle. She casts Depulso, knocking Sebastian into a wall, and then destroys Salazar Slitherin’s journal. She then grabs her uncle’s body and disappears, leaving Sebastian completely defeated.
Sebastian gets up and runs to the exit of the catacomb. You chase after him, pleading for him to stop, so you can talk about everything that just happened. Only after exiting the catacomb does he finally stop and turn to speak to you. This is when you will have the opportunity to first learn Avada Kedavra.
As Sebastian tries to explain his actions, you’ll have the choice of whether to agree with him or tell him he went too far. 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.