From the Super Mario Wiki
Retrieved from "http://www.mariowiki.com/index.php?title=Phantom_Hand&oldid=1933895"
Phantom Hands are floating gloves that point to secrets in New Super Mario Bros.. They only appear in the World 7 Ghost House, and their only purpose is to point out the location of an invisible block containing a Question Switch moving back and forth to the player. They are not enemies, meaning that Mario or Luigi are not injured if they touch one.