Tower of Doom

Mankind has been abusing mother earth. And now Earth has come to bite back.  An evil sorcerer wants to end the life of the people.  You are that sorcerer and it is your job to build some defense for your tower, giving you the time to cast the spell that will wipe out mankind.   The game is played via mouse and the idea here is to build towers that will defend the main tower.  Each tower has its strength and weaknesses.  You need to determine, which tower you should use.  Each kill will give you the mana that lets you to build more tower or upgrade an existing tower.