I was only going to get two monster manuals, I would get this one for inspiration and B/X Essentials: Monsters for reference (when certain modules mention a monster but don't provide information about the monster.)

Veins of the Earth is great, Monstrosities is great. I'm glad I have them. However, I find CC1 essential.

The very best. Nothing is quite like it, but Kidnap the Archpriest will probably outdo anything that imitates it.