public class Turn
{
    public Turn()
    {
        NextPossibleTurns = new List<Turn>();
    }

    public Turn(
        Character thanos,
        List<Character> avengers,
        int number,
        int avenger,
        Turn previousTurn)
    {
        Thanos = new Character(thanos);
        NextPossibleTurns = new List<Turn>();
        Number = number;
        PreviousTurn = previousTurn;

        Avengers =
            JsonConvert.DeserializeObject<List<Character>>(
                JsonConvert.SerializeObject(avengers));
        Avenger = Avengers[avenger];
    }

    //...
}