Horn of the Last Battle

As an Action, a creature can blow the horn,
summoning 1d4+1 Wraiths to the area.
The Wraiths are hostile to all creatures and
remain for 1 minute before vanishing.
Once the horn has been used in this manner, it
cannot be used again for 1d6+1 days.
"We need ghost stories because we, in fact,
are the ghosts."
- King Steven of the Dark Tower