stage1PlayerSaved.health = 80;
stage1PlayerSaved.position = 50.3f;
stage1PlayerSaved.color = Color.Green;

public class Player
{
public int PId;     //This will not change
public string Name; //This will not change
public int Energy;  //This may change over stanges

//you should have a method which returns PlayerInfo object
public PlayerInfo GetPlayerInfoToBeStored()
{
    return new PlayerInfo(this.Energy);
}
}

//this class will have only those information which can change
public class PlayerInfo
{
public int Energy;

public PlayerInfo(int playerEnergey)
{
    Energy = playerEnergey;
}
}

public Dictionary<int, Dictionary<int, PlayerInfo>> StoredPlayerState =
    new Dictionary<int, Dictionary<int, PlayerInfo>>();

public void SavePlayerInfo(int stageNum, List<Player> playerList)
{
    Dictionary<int, PlayerInfo> playerInfoTable = new Dictionary<int, PlayerInfo>();
    foreach(Player player in playerList)
    {
        playerInfoTable.Add( player.PId, player.GetPlayerInfoToBeStored());
        StoredPlayerState.Add(stageNum, playerInfoTable);
    }
}

public void MainMethod()
{
    List<Player> playerList = new List<Player>();
    //add players in this list

    //after stage 1
    SavePlayerInfo(1, playerList);

    //after stage 2
    SavePlayerInfo(2, playerList);
}

public sealed class GameVariables
{
    private static readonly _instance = new GameVariables();

    public static GameVariables Intance { get { return _instance; } }

    private GameVariables()
    {
        Reset();
    }

    public void Reset()
    {
       //Initialize your variables here when you start a new game
       PlayerHealth = 100;
       PlayerPosition = 0f;

       [...]
    }

    public int PlayerHealth { get; set; }
    public float PlayerPosition { get; set; }

    [...]
}

public class SomeScene
{
    void update()
    {
        GameVariables.Instance.PlayerHealth = 80;
    }
}