oop.cs

public class ServerGame : Game
{
    public override void MakePlayer()
    {
        MainPlayer = new ServerPlayer();
    }

    public void Tick()
    {
        MainPlayer.ServerThing();//Unavailable without casting
    }
}

public abstract class Game
{
    public Player MainPlayer { get; set; }
    public abstract void MakePlayer();
    public void Tick() { }
}

public class ClientGame : Game
{
    public override void MakePlayer()
    {
        MainPlayer = new ClientPlayer();
    }
    public void Tick()
    {
        MainPlayer.ClientThing();//Unavailable without casting
    }
}










public class ServerPlayer : Player
{
    public void ServerThing() { }
}

public abstract class Player
{

}

public class ClientPlayer : Player
{
    public void ClientThing() { }
}