Horde Control

This is Horde Control! A survival zombie shooter except you're the horde!

Your goal is to kill the survivor.  You can spawn zombies in the outer perimeter of the map.  The type of the zombie you spawn will depend on the zombie you've selected in the top left of the screen.  However, zombies aren't free.  You must spend some serum to create them.  Your total serum and amount of serum you generate per second are in the top left of the screen.  When the survivor kills a zombie you serum production will increase.  

How fast can you kill the survivor?