At least some content in this article is derived from information featured in Harry Potter: Hogwarts Mystery. Spoilers will be present within the article.
The horn of a Dragon was a common potion ingredient. The powdered horn of a Romanian Longhorn was highly valuable and used in many potions. However, the excess trading of it caused the numbers of the Longhorn to fall considerably, and so the horn was rated a Class B Tradeable Material. It was used in the Fire-Breathing Potion. Like most Dragon parts, it was extremely magical.