Once players complete the main storyline of Pokemon Scarlet and Violet's The Indigo Disk DLC, they can speak to a man in black named Snacksworth, who hangs out near the front entrance of Blueberry Academy. By completing BBQs and turning them in, he will gift you a random treat for a Legendary Pokemon. The [insert Pokemon name] Treat is a key item needed to encounter every Legendary --there's one Treat for each.