Demo page of CSS3 transform/transition with some JS

balloon.css

#ballon { 
  -webkit-transition: all .2s ease-in-out; 
}

balloon.html

<img src="balloon.png" id="balloon"/>

balloon.js

(function () {
  function $(id) { return document.getElementById(id); }

  var x, y, bx = 0, by = 0, angle, balloon = $('balloon');

  document.addEventListener('mousemove', function(event) {
    x = event.pageX;
    y = event.pageY;
  });

  function updatePos() {
    var dx     = x - bx - 30, 
        dy     = y - by,
        nangle = Math.atan(dx/dy),
        nbx    = x - 35,
        nby    = y - 165;

    balloon.style.webkitTransform = "translateY(" + Math.min(y, Math.abs(dx/2)) + "px) translateX(" + nbx + "px)  rotate(" + nangle + "rad)";

    bx    = nbx;
    by    = nby;
    angle = nangle;
  }
  setInterval(updatePos, 150);
})()