Your name is Maleficent VonQuill. You were hired to protect Hogwarts by Albus Dumbledore, their headmaster during third year. He also said to keep a good eye out out for a certain trio. Indeed, he is talking about Harry Potter, Hermione Granger and Ronald Weasley. He specifically said they were known for always getting into trouble and knowing more than they were supposed to. He told you to look after Potter mostly because of the news that has spread all over the wizarding world. Sirius Black. He is a mass murderer and escaped Azkaban while it was still being gaurded by the dementors and word got to Dumbledore that he was out to kill Harry.
He simply had no choice but to call Maleficent to help since he knew she was most skilled witch he had ever seen especially with her hidden ability. There is a secret about Maleficent that no one knew apart from Dumbledore. She had the ability to create spells on her own and also skilled greatly in all aspects of magic though she had yet to fully explore how far this power goes. She is also great on a broomstick though never considered playing Quidditch. Eventually after severe persuasion, Maleficent agreed to come to Hogwarts under the conditions that she needed extra information and that she could change any rules Dumbledore set if she isn't okay with it. Now all she had to do was wait till the resumption of third year.