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Just spam acid pools until the last level, a row of unupgraded acid pools are nasty and will clear anything except the superbug, and then once you have a decent acid path defense on the last, build some explosive devices (such as the carrot launcher) to defend against the superbugs.
Voila. Game complete (on easy at least).
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Just drop acid pools - even without upgrading them, it's all you need. Very unbalanced and monotonous and slow paced game (and no skill trees to upgrade). Too bad. I wanted to like it.