I finished the game and it's pretty easy. All you need for the challenges are a couple of Commander J'Ardans, Scythian Elites, and Battle Crys. It is still a little buggy and there should be a way to cancel the animations so it will go faster.
I agree with most of these comments. There are some broken physics in this game that ruin the otherwise pretty good experience. Also, if there was a key that resets the whole tower that would help too. It's a bit of a hassle to pause and restart for me when I want to make a good base.
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