Zombies are a mindless, blood thirsty race, desperate for flesh to eat. Most are under Robotguy's control, so, be good, or be eaten. Zombies can infect humans if they are not too violent, and just administer a bite or two.
They look exactly like humans, except that they are rotten and decayed. They make grotesque groaning sounds and shamble towards their victims. Some zombies look exactly like Minecraft zombies, and they infect Villagers by killing them.
"IT'S A ZOMBIE APOCALYPSE!! THEY'RE COMING!!! HELP!! HEEEEEEEEEEEELLLPPP!!!! ACKACKACKURGHGLEEAAAAAAAAARRRRGGGHHHH-- BRRRAAAAAAAAAIIIINNNNSSSSS!!!!!" ~A Villager who was victimized by zombies