One Call of Duty: Modern Warfare 3 player discovers an easy way for solo players to easily complete the typically difficult Teir 3 contracts in the Zombies mode. While Zombies has been a staple mode in numerous Call of Duty games, the fan favorite experience has seen plenty of big changes inside of Modern Warfare 3. One of the biggest tweaks from previous games is that Modern Warfare 3's Zombies experience is open world, allowing players to explore and take on the undead within the biggest Zombies map in franchise history.