The problem is it doesn't seem to horror mark people or add additional horror seeds.
I tested with 2 nations set to human and spammed it on an army filled province with one nation and observed the results with the other. I did see the horrors hatch when units died in battle but other than that, I did not observe any horror marks unless these aren't visible.
Based on the spell description is there a difference between the parasitic horrors and the original true horror?
secretperson... have you tried allowing 20+ turns to pass and then have a battle to determine if the spell actually spreads horrors to others?
NTJedi- I tried it a few times and while my testing wasn't perfect, it seemed that only one horror would pop out from the seed. Honestly, it's fine if that's all it does as I'm sure there are still uses for it. But I was just wondering if it's supposed to do more than that.