I believe the testcases's result is incorrect.

My solution:

public static string misereNim(List<int> s)
{
    var pileOfOneCount = s.Count(x => x == 1);
    var pileOfOtherCount = s.Count(x => x > 1);

    if (pileOfOtherCount == 0)
    {
        return pileOfOneCount % 2 == 0 ? "First" : "Second";
    }

    return pileOfOtherCount % 2 == 0 ? "Second" : "First";
}