Here's a trick to people who are stuck: Don't stay in that location and try to beat it. Just go to other parts of the world that are easier, and level up your zombies and get stuff from the lab. Once you are more powerful, then go back to the place you were stuck on.
 "Flaming Zombooka"){kind=icon}
 "Creeper World Training Sim"){kind=icon}
 "Mushroom Madness 2"){kind=icon}
 "The Great Siege"){kind=icon}
 "SteamBirds"){kind=icon}
 "Civilizations Wars"){kind=icon}
 "Post it Draw it"){kind=icon}
 "Infectonator : World Dominator"){kind=icon}
 "Toss the Turtle"){kind=icon}
 "Multitask"){kind=icon}
 "CycloManiacs"){kind=icon}
 "Desktop TD Pro"){kind=icon}
 "Platform Racing 2"){kind=icon}