Ghosts are otherwordly spirits in the Skylanders series, usually Undead, living in areas of their prefered element or in villages like the Darklight Crypt. In the latter, they have moved on from eating brains of the living and now enjoy eating only pies. However, Occulous arrived and outlawed Darklight Crypt from having pies and wanted the ghosts to do terrible things to the living. After Occulous was defeated, the Ghosts went back to eating the pies made by the Molekin, Batterson.
Several ghosts seem to have varied voice patterns between them. Gallant and The Ferryman speak in a distorted double voice, Machine Ghost speaks in a robotic monotone, Smoltergeist speaks in a raspy echoing tone, and Spoooky extends certain letters, much like his name.
Cali mentioned that ghosts have the ability to scare curses away, and intended to use them to scare away the curse that plagues Monster Marsh.
Machine Ghost, Smoltergeist and Bad Juju are the only Ghosts known to be from elements other than Undead.
These ghosts appear to need to be in their own element - Machine Ghost malfunctions like his robot and is always connected to its power panel(and was un-revived by Ermit fixing the war machine itself), while Bad Juju instructs Junior to eat lightning to grow strong.