It would be better if there was a "finish mission" button instead of the mission automatically finishing. That way you don't miss out on left over stars.
So far, what I've found to be the best way to get the last achievement is to save a lot. Save every time before you make a risky decision and you can reload if something goes too wrong.
All of the levels were not too hard, so there are many possibilities for adding more difficult levels. And there should "pieces x now" count in the end level just for lols
Tip use your short bow to shoot every exploding barrel in sight. Jars give 5 money, barrels give 50 and exploding carts give 150. If you upgrade your bow a couple of times it can destroy barrels in one hit.
If you put a building on top of a ring left behind by an emitter, it gets boosted.
For example, relays get increased range and mortars get increased range and fire rate.
It would be more interesting if the opponent sent large groups of troops with breaks in between instead of the slow trickle that can be taken out easily by the crossbow.
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