Hogwarts Legacy professors have unique reactions when players cast the Avada Kedavra curse in their presence. Hogwarts Legacy lets players learn all three Unforgivable Curses, though they aren't taught by any of the professors in the game.
To learn all the Unforgivable Curses in Hogwarts Legacy, players have to complete Sebastian Sallow's quest line. Other spells in Hogwarts Legacy are typically taught by the game's professors. Completing special assignments will in turn give Hogwarts Legacy players the chance to learn new spells, which can then be utilized in combat scenarios, exploration, puzzle solving, and much more.
The professors in Hogwarts Legacy encourage players to test the spells they teach them on practice dummies in their classrooms. However, if players decide to use Avada Kedavra instead, their professors will have unique reactions. This was demonstrated in a YouTube video uploaded by user Meloo, showing a handful of the Hogwarts Legacy professors reacting to the Avada Kedavra curse.
Most of the professors in the video scold the Hogwarts Legacy student for using Avada Kedavra. For example, Potions Professor Sharp says, "I suggest you give your wand a rest. Don't let me find you doing that again." The video ends with the popular Professor Garlick telling the player that they can keep practicing if they want as long as they mind the plants, though that particular bit of dialogue is unlikely tied to Avada Kedavra.
It's possible that the dialogue in the video isn't Avada Kedavra specific at all, but rather just happens when players use any of the three Unforgivable Curses in front of the professors. Hogwarts Legacy players are free to visit their professors whenever they want throughout the day and can go test a variety of spells in front of them to see if they have any other unique reactions besides when one casts an illegal curse.
Players could also experiment with other characters around Hogwarts Legacy's open world, casting Avada Kedavra near them to see if they react similarly to the professors. There are plenty of friendly NPCs spread throughout Hogwarts castle, Hogsmeade, and the greater open world, though players can't go on Grand Theft Auto-style killing sprees with the curse. The game simply won't let players cast Avada Kedavra or other offensive spells on innocent people, so they're reserved for use on enemies.
Hogwarts Legacy is out now for PC, PS5, and Xbox Series X with PS4 and Xbox One versions releasing April 4 and a Switch port dropping July 25.