Yes it does launch Parasitic horrors or at least the first one horror marks others dunno for sure if you get yet more of the parasitic horrors that Horror mark even more commanders, and it does seem to be somewhat effective. Last turn I quarantined all horror marked commanders able to move into their own province and sent one of the telastic animations into the Forgotten city in hopes they would die, This turn I lost a Naiad to a horror attack and found yet another commander horror marked in the original province.
Perhaps my horror marked Naiad was attacked because I moved her from her home province and according to the spell description your not supposed to do that but I imagine it would have happened regardless. After all I think the horror attack would have actually happened before she had a chance to move.
But at least the telastic animation found 1484 gold in the Forgoten city.
Re: Horror Seed on Immortal commanders
Guess I got beaten to that punchline. 
Linear Mode
