Ministry of Magic classifications

Within the Ministry of Magic, the Department for the Regulation and Control of Magical Creatures created a system of rules to determine whether a magical creature was a "beast or being" and also gave each creature a classification in terms of how dangerous it was - or not! The rating was measured with "X" being the least dangerous and "XXXXX" being the most dangerous. So, a Flobberworm, for example, would be rated X, while something far more scary, such as a Chinese Fireball dragon, would be XXXXX.