The Zombies come in increasingly large numbers and strength over a period of several rounds.
The zombie originally were an olive green, with glowing yellow eyes and Nazi Uniforms (add picture), but was altered to a modified version of the original Minecraft zombie skin. (add picture)
Each zombie killed gains you points, the amount of which varies by difficulty:
Easy - 150 points
Medium - 100 points
Hard - 50 points
Each round, the number of zombies,their power and health grows.
It is unknown how and why there are zombies, as there is no official storyline released by Modzilla as of yet.
Every 6th rounds, hellsheep also spawn.