using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var array = new string[] { "key1###value1###MyTitle_reporting_123###value2", "MyTitle_reporting_123###value3" };

        var flatList = array.SelectMany(x => x.Split(new string[] { "###" }, StringSplitOptions.None));

        var keyValueTuples = flatList

            .Zip(flatList.Skip(1), Tuple.Create);

        var titles = keyValueTuples

            .Select(x => x.Item1)

            .Where(x => x.Contains("MyTitle") && x.Contains("_reporting_"))

            .Select(x => x.Replace("_reporting_", ""));

        Console.WriteLine(string.Join(",", titles.ToArray()));

    }

}