You can speak and read common and one other language of your choice. 

When determining your character’s ability scores, increase one score by 2 and increase a different score by 1, or increase three different scores by 1. Follow this rule regardless of the method you use to determine the scores, such as rolling or point buy. The “Quick Build” section for your character’s class offers suggestions on which scores to increase. You can follow those suggestions or ignore them, but you can’t raise any of your scores above 20.

your size is medium

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

Like all Dullahan born without a neck your able to remove your head from your shoulders. 

When your head is detached from your body you can use the senses of your head, while your head is detached your body is blind, deaf, and mute, but it is able to move and feel sensations. 

Using your natural connections to the dead you can reach out to them to answer your questions. 

Twice per long rest you can cast speak with dead without using a spell slot