Syntactic Sugar for moving MCs

1 
MovieClip.prototype.move = function(direction, speed) {
	switch (direction) {
		case "up":
			this._y -= speed;
			break;
		case "right":
			this._x += speed;
			break;
		case "down":
			this._y += speed;
			break;
		case "left":
			this._x -= speed;
			break;
	}
}

// allows:
hero_mc.move("left", 5);

Just to make your code that bit more readable and DRY.