Any advice how to get this one? I have tried a few combos using the 10k limit mode but no joy. One wave always gets through. Any particular map/strategy to get this?
Thanks.
I got this achievement last night without trying. Barrier to Entry made it extremely simple. I used level 3 gun towers and a well-placed temporal tower and none of them got through. Just make the aliens go up north towards the exit, have a temporal near that ramp, then make the aliens come back down toward the entrance so that the gun towers there get 2 chances at them. Nothing got past.
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I just did what this guy
Got this achievement on Barrier to Entry
untouchable