Your Constitution score increases by 2 and your Dexterity score increases by 1

Dullahans are a race of fey strongly connected to the Shadow Fell. The essence of the Shadowfell permeates their beings and guards them against the passage of time. Dullahans do not age, cannot be forced to age though magic and never has a Dullahan been known to die from old age. 

Dullahans have an innate fear of gold and grow wary in the presence of it, preferring their payment in the form of gems, magic items or platinum. If a Dullahan touches or has gold forced upon them they lose all strength in their body and become unable to move or stand effectively. For every round you touch gold take 1d4 necrotic damage and you are knocked prone until no longer touching the gold

At 1st level you can cast the spell "Find Steed" at will without expending a spell slot or needing a long rest. The time to cast the spell is also reduced to a action. At 15th level you can cast"Learn Name" and at 20th lvl "Dullahan Name Calling" once per long rest. Wisdom is your spellcasting for these spells

Dullahans have the amazing ability to safely remove their own head from their body. While their head is detached from the body Dullahans cannot speak except when casting "Dullahan Name Calling". When a Dullahans head is more then 60ft away from its body they get a sense of its direction at all times as long as its on the same plane of existents and is consumed with the need to reunite with it becoming violent at times if separated for too long.

You have proficiency with polearms

You have proficiency with thieves tools

While attached any damage dealt to your head is taken as if it has vulnerability and goes flying ( Distance = Strength Modifier of the creature that hit 2x)

Your head has 60ft of darkvision

Your headless body has 30ft of blindsense

Dullahans can take the form of any race, from a simple human being to a more exotic Genasi. Dullahan takes on the form and physical features of that race perfectly but do not retain their more base functions and abilities. For example, a Dullahan in the form of a Dragonborn will lack the breath weapon each Dragonborn is granted at birth or a one resembling an elf will not have the knowledge of weaponry or magic the elves learn at a young age.

You speak, read and write common and one language of your choice. It's common that a Dullahan will choose to speak the language of the race it most resembles to keep up appearances