[silin]

да просто все, на самом деле:

link = null;
trace("mc"+link);//mcnull
deg["mc"+link].gotoAndPlay("s2");//≡deg.mcnull.gotoAndPlay("s2");
link = 5;
trace("mc"+link);//mc5
deg["mc"+link].gotoAndPlay("s2");//≡deg.mc5.gotoAndPlay("s2");