No matter what the conditions, the Dullahan can see very clearly as the Dullahan has no eyes (its headless)

The Dullahan is known to arrive in a carriage that appears from a dense mist. It is assumed that the Dullahan itself calls this fog to disguise its location

Gain bonuses to Strength Dexterity, Intelligence and Wisdom (all +2). However the Dullahan is not very charismatic due to its lack of head and proper speech. Therefore it suffers froma  permanent disadvantage to charisma checks, rolls and saves.

The Dullahan is a composed creature. It only has access to the rage ability when activated by Headhunter. It does not have access to regular rage. 

The dullahan can summon a scythe from the fog as a bonus action. It functions as a regular scythe and can be dismissed with a bonus action or by dropping the scythe.

Due to the Dullahan's lack of an actual mouth, it can communicate its intent to any being through a bizarre telepathy. However, anyone talking to a dullahan would swear on their grave that they spoke out loud the entire time. The dullahan cannot understand all languages. Just communicate its own 'speech' to all beings.

Your size is medium. Rgardless of height chosen. Anything from 6ft to 8ft is accepted as the height for a dullahan.

Insight, Perception, Investigation and Arcana

Wisdom, Constitution and Intelligence

Dullahans do not age, they live indefinitely. Some believe they are immortal as so few have been killed