No no, I don't mean L4D style evolution. For those of you who survive long enough, I'm sure you've noticed just how trivial zombies become when you've wiped the vast majority of them out, especially when - after some time - they become slower and weaker due to decomposition. Now I don't have a problem with that, in fact, it reminds me quite a bit of the Walkin Dead and how the cast of the show, over the period of the series, stop noticing the zombies in the background as they adapt to the post-apocalyptic lifestyle. However, for people looking to maintain that zombie-fueled terror and make things a little more challenging, I suggest this; In the 'Zombie Lore' category, specifically under Decomposition, why not add an option which causes zeds to increase in difficulty? Becoming stronger, or faster, or more adept at tracking you down - or all of the above. Something that causes individual zeds to become a bigger threat when the overall population of the undead begins to decline.