If a contaminated area exists, you should concentrate on removing it. This is because if the contaminated area remains, regardless of the mission type, the mission can not be completed. If you kill a zombie or deploy a soldier from a cube with a contaminated area and close that cube, the contaminated area will remove. Cubes that do not have contaminated areas should be avoided as much as possible to complete the mission.
Different types of USTF troops and zombies have varying levels attack and defensive powers respectively. Cubes with red numbers indicate there are tough zombies surrounding the cube. Attacking tough zombies with troops with a lower attack power will not kill them and will infect the troop. A more strategic attack is required when attacking tougher zombies with a high level of defensive power. Co-op Attack Deploy multiple troops first and then seek out a tough zombie to perform a co-op attack. This will deal aggrgate damage of all the deployed troops. Helipcopter Attack Attacking after deploying 8 or more troops will unleash helipcopter attack. Troops with a higher power Attack Attack with troops with a higher attack power than the zombie's defensive power.
Bosses encountered after chapter 2 has high defensive powers. It's very tricky to deal with because it has special abilities, and it moves and hides its location. Here are some tips on seeking out and attacking boss zombies. Exclude the surrounding of black numbers Red numbers on a cube indicate there are tough zombies surrounding the cube. I.e. black numbers means there are no boss zombies surrounding the cube. Block the boss's movement path Since boss zombies can't move to a cube that has been cleared, try to limit its movement by clearing surrounding cubes where are likely to be hiding. Use Items Try using special attack items such as helicopter strikes or zombie lures at locations where they are presumed to be hiding. Co-op Attack If you have pinpointed its location, deploy as many troops as you can and perform a co-op attack.
Seeking out 8 or more zombies and deploying a troop will trigger a helicopter air strike. Chain Gun (x2 attack force) If 8 to 13 zombies were found, a chain gun initiates an attack. Missile Attack (x3 attack force) If 14 or more zombies are seeked out first, a missile launch attack is initiated. Since this is an effective strategy when attacking tougher zombies with high defensive powers, seek out as many zombies as you can before deploying a troop.
The numbers showing on the cubes represent the number of zombies surrounding that cube. There may be up to six zombies surrounding a cube. Try and deduce the location of a zombie by inferring from all adjacent cubes. The number displayed on a cube changes when zombies are found. When zombies are found, the troop immediately launches attack. Cubes with red numbers indicate there are tough zombies surrounding the cube.
When communication towers, marts, gas stations, etc. appear, you should concentrate around the area. All zombies in the cubes surrounding the area are killed, and occupation is completed. Minimizing the use of cubes other than surrounding the area to be occupied is advantageous for mission completion.