[Solved]-Adding new data to highchart tooltip-Highcharts

You can attach the additional data with each point in the series.data as follows

series: [{
    name: 'Series 1',
    data: [{
        y: 2,
        players: ['a', 'b']},
    {
        y: 3,
        players: ['a', 'b', 'c']},
    {
        y: 2,
        players: ['x', 'y']},
    {
        y: 4,
        players: ['a', 'b', 'c', 'd']}
    ]
}]

Now in the tooltip.formatter you can consume the additional data as follows

formatter: function() {
    var result = '<b>' + Highcharts.dateFormat('%A, %b %e, %Y', this.x) + '</b>';
    $.each(this.points, function(i, datum) {
        result += '<br />' + datum.y + ' players online';
        $.each(datum.point.players, function() {
            result += '<br/>' + this;
        });
    });
    return result;
}

Complex tooltip | Highchart & Highstock @ jsFiddle