Another person and I tried to do the zombie fest #4 ( be the zombie mode ) but we couldn't do it. Is there a particular way of doing it? If anybody has done it on gog please let me know.
I'm playing with "Invasion" on, I thought it would choose a Zombie at random. I could be wrong. I think it's also based on the frequency of the Invasion, maybe you should try setting it to every night, instead of every three nights.