While playing this mode I wondered, why apostles, inquisitors or a new type of religious unit - exorcist of some kind or so, couldn't remove the taint from the soil in friendly territory, so this constant headache would stop and you could concentrate into pushing them back on the outskirts? You would still be vulnerable to zombies raised by a spy action, but at least cleansing the ground would fit into this common loop in games, where you have a constant and nagging problem which must be dealt manually at first ,but then you do some progress and automate and remove it or solve it to a significant extent.
I think this is a BRILLIANT idea! Would make getting a religion worth more going for it in this game mode; I'd say give Apostles the ability to cleanse soil, consuming all their charges in the process as if you're Evangelizing your beliefs.
Other tweaks I propose:
1. A timer for units that have died in a particular tile. The chances of spawning a zombie reduces with turns, and additional reduction with passing era - such that you can pretty much get 0 chance after about 3 eras.
2. cities where traps and barricades are made will trigger a lens (integrated into the Religion lens) showing where zombie spawns are possible. Upgrading these improvements will give you more information on the chances, such as percentage chance, a warning of an eminent uprising within the city 3 turns before the zombie unit spawns, or a warning that an enemy spy is doing an operation to spawn zombies in your city.
3. Zombies cannot spawn on tiles adjacent to a barricade on the side between the barricade and the city centre.
4. Additional interactions with the other game modes. For example:
- Soothsayers can spend charges to kill all adjacent zombies and can cleanse soil where a unit died
- zombies cannot spawn in a city with Ley Lines, Vampire Castles or Old God Obelisks. Additional damage to zombies by vampires. The Guilded Vault unlocks a project that causes your entire empire (including units) to be immune to zombie attacks for 20 turns. Every zombie killed grants gold and faith equal to half the zombie's combat strength
- heroes get +10 combat strength against zombies. Zombies get -5 combat strength for each adjacent hero
5. Balance the starting combat strength of zombies, behavior etc...