Fey mounds are hidden burial grounds of wild fey. When a fey creature dies, it is placed in a mound and covered loosely with earth, branches, and leaves. Mushrooms grow around such mounds, and lights, ghostly giggling, and fey apparitions are common near or on them. Powerful magical treasures, the former belongings of the dead fey, are often placed in the mound.
Effect: A nearby creature that makes a DC 27 Arcana check can sense a fey mound. Fey mound soil is a powerful component in fertility rituals. Some mounds act as fey crossroads. Most are trapped, and some are guarded by living fey. Those guardians gain a +1 bonus to any one d20 roll they make each round while guarding the mound.
Usage: Use a fey mound’s strange phenomena (strange lights, calling voices) to draw the characters into the area of a fey mound. Have the buried fey creature’s spirit rise to confront the characters. Depending on their interaction, the spirit either imparts useful knowledge or its former belongings, or turns into a vengeful spirit, such as a banshee, and attacks the characters for disturbing the burial site.
Published in Forgotten Realms Campaign Guide, page(s) 53.