Edit in JSFiddle

$(function(){
    $('#btn').hover(function(){
      $('#target').slideToggle(1000);
    }, function(){
      $('#target').slideToggle(1000);
    });

});

<div id="btn">BTN</div>

<div id="target"></div>

#target {
    width:100px;
    height:500px;
    background:#333;
    
    position:absolute;
    top:10px;
    left:150px;
}