9. Van Richten’s Guide to the Ancient Dead
2nd Edition
Ravenloft
1994
This supplement took a minor enemy from the basic enemies (the Mummy) and turned it upside down, and created one of the most intricate enemies you can have. A lot of the book is fluff, but what it does have is a lot of meat for creating interesting, unique, and powerful undead creatures. It creates scales of power, interesting abilities, and more.