Another use of the Day of the Dead Marigolds is to see a couple of hidden ghosts sneaking around Azeroth. The Unseen of Raven Hill for example can only be seen when the veil is pulled aside.
The poor lingering dead of Duskwood, their presence unfelt (unless you are in the habit of aoeing empty houses) by the living still wander the ruins of their homes. Makes you wonder how many other “hidden” features there are scattered around Azeroth.
My warlock might have to go a wandering with detect invisibility.