Spirits

From Animal Crossing - Wiki on Neoseeker

Spirits are a non-villager species that have appeared in all versions of the game. They are defined by their ghost like appearance and difficulty to find.

Name	Games	Appearance	Information	Work Place
Serena	Animal Crossing: City Folk		Serena will give the player a Golden Axe if they talk to her the right way.	Infests the town fountain.
Wisp	Animal Crossing Animal Crossing: City Folk		Wisp is a ghost who can help players when they find him. He can give the player rare items, clear their home of cockroaches, and clear all weeds.	Helping players who release him from his captivity.