The guiding principle behind my setup is to spread out the two groups, and funnel them past a gaggle of typhoon towers and a blizzard in the center of the map. I start by building the maze with pea-shooters, sell one and upgrade to a squirt, upgrade it all the way to typhoon, and then nothing can get through for a few waves. That gives me time and cash to make a blizzard tower and more typhoons. I think my best score had two freeze towers, one to freeze each flying boss.
Spawns are the toughest, but they move slowly; I tend to hurry up the flying wave so I can shoot them down before the spawn get in range.
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