Tips: replay easy levels to get all upgrades, then with just super towers you will get till lvl 26, after that, the only tactic i found working is to send out all waves immediately then hold 'z' key and click really fast. But lvl 35 is still impossible that way. There you must use some megabombs also, with the right timing, just watch the money. On bomb levels 1-2 super towers is all needed (near end of path)
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 "mini Tower Defence (mTD)"){kind=icon}