Reverse Decomposition, or Composition if you will. Essentially add an option for zombies to get stronger over time. 3 options ideally. Time increases: Speed, up to runners. Strength, up to superhuman. Or both, up to death incarnates. We already have an option to stop decay, so why not have an ever increasing threat. And on that note, a modifier to determine how long until 'max' decomp (Or comp) effects are reached? Like 1 week, 1 month, 6 months, 8 months, 1 year, etc. I'm doing something similar in sandbox and it's pretty fun. I'm using the respawn to (If I did it right) start with no zombies and by day 100 I should have Class 4 populations of zombies!