void fill_listbox()
    {
        string constring = "datasource=localhost;port=3306;username=root;password=xdmemes123";
        string Query = "select * from life.players ;";
        MySqlConnection conDataBase = new MySqlConnection(constring);
        MySqlCommand cmdDataBase = new MySqlCommand(Query, conDataBase);
        MySqlDataReader myReader;
        try
        {
            conDataBase.Open();
            myReader = cmdDataBase.ExecuteReader();

            while (myReader.Read())
            {
                string sName = myReader.GetString("name");
                namelistbox.Items.Add(sName);
            }
        }catch (Exception ex)
        {
            MessageBox.Show("Something went wrong. Error copied to clipboard.");
            Clipboard.SetText(ex.Message);
        }
    }

List<string> playerNames;

void fill_listbox()
{
    string constring = "datasource=localhost;port=3306;username=root;password=xdmemes123";
    string Query = "select * from life.players ;";
    MySqlConnection conDataBase = new MySqlConnection(constring);
    MySqlCommand cmdDataBase = new MySqlCommand(Query, conDataBase);
    MySqlDataReader myReader;
    try
    {
        conDataBase.Open();
        myReader = cmdDataBase.ExecuteReader();

        while (myReader.Read())
        {
            string sName = myReader.GetString("name");
            playerNames.Add(sName);
        }

        foreach(string name in playerNames)
        {
            namelistbox.Items.Add(name);
        }

    }catch (Exception ex)
    {
        MessageBox.Show("Something went wrong. Error copied to clipboard.");
        Clipboard.SetText(ex.Message);
    }
}

void textBox_TextChanged(object sender, EventArgs e)
{
    // create filtered list from playerNames
    var filteredList = from name in playerNames
                        where CultureInfo.CurrentCulture.CompareInfo.IndexOf(name, textBox.Text, CompareOptions.IgnoreCase) >= 0
                        select name;

    namelistbox.Items.Clear();
    foreach (string name in filteredList)
        namelistbox.Items.Add(name);
}