It's time for a good ol' fashioned tower defense game. Your tower is under attack by a horde of zombies. Using your mouse, aim arrow units to shoot them dead before they can get to your tower in an attempt to destroy it. Surviving for long periods of time will earn you upgrades and level-ups to help combat the attackers.
When starting a game, make sure you play Zombie Invasion mode, not Campaign nor Boss Trials. Your final score will be determined by how long you can survive. Whoever can survive the longest will move on.
You have until 5 PM on Sunday to submit your best time. Extensions will only be given if both parties agree to one.