I've learned the hard way from DMing Princes of the Apocalypse for my podcast gg no re how NOT to run a black earth priest (p195-6). Let my humiliation teach you how to TPK.
The two places I know of that you will run a black earth priest are:
- Levels 1-3: Tomb of Moving Stones (p153, area 9, Larrakh)
- Levels 3+: Sacred Stone Monastery (p59, area 6/9, Qarbo)
Here's what you should do:
- First: cast spider climb and get up on the ceiling
- cast shatter at the highest level you can, doing up to 4d8 in 10' radius, save 1/2
- if you're hit, use your reaction to cast shield
- if you need to jet, cast expeditious retreat and hit them the next day
It's very simple, but listen closely: slow is a trap. Each time I've led with that, and each time I've been disappointed. Even if everyone fails the save, they get to make new saves at the end of each of their turns, and your save DC is only 13. And generally your black earth priest isn't going to be leading a bunch of hard hitters who would benefit from the support.
Trust me: shatter them repeatedly and without remorse while you're running around on the walls and ceiling.