Build towers to defend the town center and upgrade them to more advanced tower types. These towers are capable of protecting more with powerful weapons. It applies to fire, ice and lighting magic towers.
Protect your communication tower against the enemy air strike. The earlier you take down enemy planes the more money you will get! You can buy or upgrade weapons for earned money and try to keep your tower safe as long as possible.
Monsters must protect San Francisco or even the world from these evil aliens. Place your monsters around the map to defeat the incoming waves of aliens.