You all say you have to pay for badges, you don't, you just have to be really patient. and for the most part the badges aren't made easier by paying except the last 2
@Trentkidd, the easiest thing for level 18 i found to do was treat it like a zone without any holy/bog, and just at the beginning of each wave knock out the bog tower for the entire level, and then heal your units and quake the other towers as you see fit, probably waiting till later levels. This worked all the way to gold for me.
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