Dullahan are mercenaries of the Fae world.
Dullahan are hired to carry out certain brutal tasks. Over the millennia, they evolved the ability to remove their heads, like the Headless Horseman, and use it to throw fear into their victims.
The Dullahan are hard to stop. One Dullahan was shot and showed no signs that it had sustained any injury. However, they can be killed if an injury is serious enough to cause death. Bo killed one by stabbing it in both sides of the chest with a broken mop. Their removed heads remain a crucial weakness: Kenzi killed a second Dullahan by dropping its head into a flaming barrel.
Will, a Will-o'-the-wisp, hired Dullahan to recover the treasure that was stolen by a human. When he found out the human was his previously unknown son he could not call off the hit because when a Dullahan takes a job they follow through on it.
- The Irish dullahan (also Gan Ceann, meaning "without a head" in Irish Gaelic) is a type of unseelie fairie. It is headless, usually seen riding a black horse and carrying his head under one arm. When the dullahan stops riding, it is where a person is due to die. The dullahan calls out their name, at which point they immediately perish.