Random day/night and terrain for each level. Added visible bullet trajectories and sound effects. Zombies will attack killing robots, creating a three-way battle; Tongue Zombies can bite and pull you from a distance, Breeder Zombies hatch minions, and Brute Zombies have self-healing shields; human levels feature high-speed self-healing Enhanced Hunters. Early reload and fire rates are slower, make good use of upgrades.