Hogwarts Legacy has a slew of side quests for you to tackle, many of which are rewardable with treasures and Galleons. Many of the world's treasures will be given to you by your classmates, but some will be discovered by exploration the world. One such quest is found in Hogsmeade, and is given to you by a goblin named Garnuff. His previous Mooncalf has been taken by poachers, and you need to get it back
In Hogwarts Legacy, there's a walkthrough for Take the Biscuit.
Before you can begin this quest, you will need to complete the game to the point where you have met Sebastian in Feldcroft. Run to Hogsmeade and you will find Garnuff below the bridge that leads to the Magic Neep. Talk to him and he will ask you to retrieve his beloved Mooncalf named Biscuit from some poachers who kidnapped them some time back.
Continue your journey to the northeastern part of the map following Garnuff's suggestion. The camp you are looking for is just east of the East North Ford Bog Floo Flame fast travel point. If you have the point unlocked, you may easily go there in a hurry. Use your broom to reach the area quickly.
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The camp is packed with dark wizards, so make sure you have Wiggenweld Potions before you go. Biscuit will be trapped in the large cage in the camp's center, and you will have to chase him down and capture him with your bag. The Arresto Momentum spell is very useful for this task.