Tweening Using Flash's Built In Tweens

First you need to pull in tween classes:

import mx.transitions.Tween;
import mx.transitions.easing.*;
this.lvlTween = new Tween(targetMc, "_y", Bounce.easeOut, -400, 200, 30);
tweenInstance.onMotionFinished = function() {
// ...
};

For more info, search for "Using the Tween class" in Flash help