You gain +1 in Dexterity and +1 in Charisma. 1 ability scores of your choice.

Dullahans reach physical maturity in their early twenties, but, similarly to elves, are not intellectually considered an adult until much later in their life, typically around 200 years old. They do not die of old age. They are effectively Immortal unless killed

Dullahans typically tend to be taller and more imposing than most humans 6-7 feet generally. 

Dullahan’s Fey nature gives them 60ft of Darkvision

Dullahan’s have advantage on saving throws against being charmed, and magic can’t put you to sleep.

Dullahan’s don’t need to sleep. Instead, they meditate deeply, remaining semiconscious, for 4 hours a day. (The Common word for such meditation is “trance.”) While meditating, you can dream after a fashion; such dreams are actually mental exercises that have become reflexive through years of practice. After resting in this way, you gain the same benefit that a human does from 8 hours of sleep.

Dullahan’s are proficient with the intimidation skill.

Dullahan's receive few blessings in their lives. The first at is they are gifted a phantom steed for them. Their steed works like the spell Find Steed, but is a singular war horse bonded to its rider. It can be placed in a pocket dimension and summoned like find steed says but be warned if you should misuse your steed. They dislike dying  

The second is the ability to cast the spell Misty Step(once per long rest)

Harbinger’s Blessing is not gained until Level 3 

Due to the detachability of their head Dullahan’s cant be decapitated except by magic so when that happens they have smoke coming from the top of their head acting as their sight and brain but they are unable to talk directly so must write everything down or use their telepathy. 

When the dullahan is headless rising smoke from the neck attaches to the head. When detached the body becomes the main head but due to their connection they share hit points. 

If the head is ever separated more than 60 ft from the body the body mind has amnesia and loses is memories. It will never stop hunting for its head. It can tell a vague area where its head might be, like with in a city but will not have any information until the connection is back with in 60 ft. 

A hit on a separated head is an automatic crit.