Dullahans are from the same place as the Sidhe Folk, but they are not quite the same being. While the Sidhe Folk are often talkative and willing to communicate with humanity, their primary danger is their desire to manage etiquette. The dullahan on the other hand are almost completely silent, only the whinny of their horses, the beat of their hooves, and the creak of their coaches allow the wary traveller to notice the sound of the approaching dullahan.
Dullahans are most often seen as black riders, typically riding a large black horse (sometimes two or four horses, but only rarely) pulling a funeral coach. Their body is always covered in a large black cloak, typically with a hood pulled high. The hood will sometimes fall back showing the creature's head is not upon its shoulders. They are typically held by the hair by the dullahan, or kept on seat beside them. If a dullahan ever loses its head, it will carve one from the turnip or gourd and carry that in its place.
If the dullahan has been on this world for long enough that its coach wear, it will repair it using human bones. The dullahan will find victims, kill them, and take their bones to repair their coach. Rarely, a dullahan will have been avoided long enough that its coach has worn to destruction, it will ride out upon one of its horses, continuing its grisly work.
You see, Dullahan believe they have the sacred duty to make sure that those doomed to die obey the strange will of their unknown wyrd. No god claims to endorse the beliefs of the dullahan, but they have a list of those they believe should die. When the dullahan is ready to take a life, they will bring forth an axe, and attempt to decapitate their victim. They do not like doing battle directly - they prefer to wait for their victims to submit to them. This means they will often attempt to sneak up behind them, use fear to paralyze them, or work with others to bring them to a place where they can be killed. For specific victims, as many as five dullahans have been known to work together to perform macabre silent plays to entrance a victim, and then have one of their number strike the head from the victim.
Once they have the corpse, the dullahan will place their victim in a coffin and bury them with as much ceremony as possible, often attempting to enlist the aid of local priests. It is common they are killed by monster hunters or heroes during this time, though some have claimed it is sacrilege to kill someone seeking a rightful burial.
Black Horse: The Dullahan has a black horse which is from the same place as it. This horse is not fully alive, and if the dullahan dies, so does the horse. The horse does not have a mind of its own but has B8 in all of its attributes and no skills (except Cart and Rider training). A dullahan who has managed to give burial to at least four people will have two horses, and one that has given burial to twenty victims will have four horses.
Detached Head: The dullahan's head does not seem to be how it sees, speaks, thinks, or eats. Instead the head is simply an accessory the dullahan carries. However, if someone manages to steal or harm the head, the dullahan takes a -2D penalty from everything, as if it had a permanent midi wound. It can find a gourd or turnip and make an Ob4 sculpture check to create itself a new head, and, once that's done the penalty reduces to -1D until the dullahan can recover its head (assuming it is not destroyed).
Not Of This World: The dullahan is not truly of this world. It is from the same place as a Sidhe Folk. This trait means that any effect or power that would affect a creature with Spirit Nature can affect the dullahan. Also, anything that would affect or drive off the undead would do the same to the dullahan. They are neither spirits nor undead, but they are enough like both that it is immaterial.
Silent: The dullahan does not make any noise, but its horse and carriage might. When the dullahan attempts to use Stealthy, nothing that would give a bonus for being able to hear will applies, since it simply does not make noise.
A Burning Wheel Monster Every Week