a good tactic i used to get the 200 kills in survival mode is to buy the [FN SCAR]-5000 exp, then buy the [hollow points] power up-1500 exp and finally buy [maximum base hp + 250]-2000 exp and then buy [maximum base hp + 25]-200 exp until you have no more exp left. Then perform a figure 8 pattern around the base aiming for the enemies that are attacking the base, enemies that are infront of you and enemies that are nearly touching you.
 "The Endless Zombie Rampage"){kind=icon}
 "Take Something Literally"){kind=icon}
 "Bloons Tower Defense 3"){kind=icon}