In this guide, you will find where to get Unicorn Hair in Hogwarts Legacy.
First, you will need to make your way to Unicorn Den, north of Hogsmeade and inside the Forbidden forest.
It is recommended to change the difficulty level to story mode so you can catch it quickly. Just fly to this location on your broom, grab your bag, and find the Unicorn. You can use a nab sack to capture the unicorn.
After that, head back to Hogwarts and go to your room of requirement, head to any vivarium, then open up your menu and place your unicorn there. Feed it once with the Beast feed and then use the brush to brush it. You can also put the feeding basin in so that your creatures are already going to be fed when you come back.