Zombies with a random coefficient that is multiplied into all of their stats (like speed, physical size, hit points, damage, and currency reward on kill).
Being able to purchase specific pregenned "air drop" kits using kill currency, like buying a "wood" kit which contains things like hatchets and wood, a "metal" kit with HQM, metal frags, pickaxes, et cetera. If things like axes, hammers, pickaxes, et cetera, are removed, being able to buy single chainsaws or jackhammers would also be good.
Player speed being reduced as zombies get closer, for each zombie, to mimic being mobbed and grabbed.