Wonderful work! I really appreciate the in-depth notes on the logic behind the choices for every single creature, and not avoiding some of the "well that just sounds unplayable to me" cases. I'm positively bursting with character ideas now, eager to let my players become mummies, vampires, succubi, lizardfolk, swarms (!) and more. Haven't tried at the table yet; as written this is amazingly balanced and nuanced, down to whatever minor aspect of the monster statblock your players might be keen on.
[5 of 5 Stars!]