The Guard Monkey is an agent. It costs 100 Monkey Money. It asks bloons for the password, and if they don't know it, it destroys them. No one knows why any of the bloons know the password, but lots of them do, so they get through. The Guard Monkey destroys two out of every five bloons that pass it. Guard Monkey Pro has harder passwords, so less bloons know it and it destroys three out of five. You get it if you play 20 games with Guard Monkey.