Marlo_Stanfield
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In my opinion, this is cheating. In a fair SoD scenario, there are 6 stacks of 25 units, and the wall's ticking damage isn't enough if less than 8 level 14 units were used in SP. I tried to generate a save with a minimum of 8 level 14 units for Luna in SP – no luck, I couldn't get more than 6.
So, it's definitely possible, but it might take weeks or months.
Added after 17 minutes
As an alternative, you could try removing a few fairies. This might help to split the harpies into 7 stacks.