I recently spent ninety-eight dollars to buy a copy of the "Harry Potter Encyclopedia" and wrote it to share with you the bad things that happened to those people in the past.
The first reason for writing this is to share it with everyone, and the second reason is to popularize my knowledge (actually, I was fooled by Baidu and Wiki). I will take you into the inside story and the key points of writing fan fiction.
It contains information about wizards, portraits, the bad things that happened before Hogwarts, the political battles in the Ministry of Magic, the law, organizations, the Encyclopedia of Magical Creatures, the Encyclopedia of Spells (more than two hundred), etc. There is always nothing you can't see, only things you can't think of.