Effect: Calling upon fell powers, a witch can place a hex on a creature within 60 feet that causes its sleep to be tormented by terrible nightmares. This functions as the spell nightmare each time the affected creature attempts to rest. A Will save negates this effect. If the save is failed, the target must make a new save each night or be unable to rest.
Advanced Player’s Guide. Copyright 2010, Paizo Publishing, LLC; Author: Jason Bulmahn.