when using the freebie tower (the one that does massive damage for 10 seconds and disappears), you should disable the ability to send the next wave. If you mass-click next wave and place the freebie tower near the spawn point, you gain massive gold and complete the game in less than 10 seconds. Other than that, it is a well done TD.
 "Zombie Splatter"){kind=icon}
 "Mini Castle Defense"){kind=icon}