[MrPoma]

class MyMovieClip extends MovieClip {

	function MyMovieClip(){

	};
	
	public static function create(parent:MovieClip, name:String, depth:Number, init:Object):MyMovieClip {
		var mc:MovieClip = parent.createEmptyMovieClip(name, depth);
		var constructor:Function = MyMovieClip;
		mc.__proto__ = constructor.prototype;

		for(var item:String in init){
			mc[item] = init[item];
		};
		constructor.call(mc);
		return MyMovieClip(mc);
	};
};

Юзать:

var myMc:MyMovieClip = MyMovieClip.create(this, 'mc', 0, {_x:100, _y:100});