This any good?
If each movieclip has an addEventListener(MouseEvent.CLICK, click) event then that reference is passed to click as event.target. Not sure what this default type is (Object?).
Anyways i think you need to cast it to say event.target is a Movieclip and then play that casting.
function click (event:MouseEvent): void
var movieClip:MovieClip = MovieClip(event.target);
function click(event:MouseEvent): void