using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp3
{
    class Program
    {
        static void Main(string[] args)
        {
            Game2D game = new Game2D();

            game.level = new Level2D();

            Console.WriteLine(game.level.DummyMethod());
            Console.WriteLine(game.level.MoreDummyMethod());
        }
    }
}

abstract class Game<T> where T : Level
{
    public T level;
}

class Game2D : Game<Level2D>
{
}

abstract class Level
{
    public string DummyMethod()
    {
        return "Level.DummyMethod()";
    }
}

class Level2D : Level
{
    public string MoreDummyMethod()
    {
        return "Level2D.MoreDummyMethod()";
    }
}