Monkey Zombies are originally monkeys trained to serve as entertainment. However, Mental obtained them and repurposed them to become members of his army. Because of their skills, Monkeys appear by climbing on the wall in order to ambush their target. They are usually deployed in large numbers in order to overwhelm their enemy.
The Monkey only has a melee attack with its knives. It can use it either if it the target is next to the Monkey if by swinging its knives downward while lunging at something.