You're fine with the Standard version and your event to note approach will work.
Presumably these Sprite and Popup Mediators are dynamically named. So tie the two mediator names together with a common postfix, such as 'SpriteMediator-12' and PopupMediator-12'
When the SpriteMediator sends a note to the PopupMediator, have it pass its name as the type parameter like: sendNotification(ApplicationFacade.SPRITE_MOVE, point, this.getMediatorName())
Then have a parsing function in the PopupMediator that returns the postfix from a string.
And in the PopupMediator's handleNotification switch, in the case for note.getName == SPRITE_MOVE, check the postfix before acting like: if (getPostfix(note.getType()) == getPostfix(this.getMediatorName()) { // update popup coords from Point passed in note body}
Hope this gets you to the finish line
-=Cliff>