You can read and write in Common (You can speak Common if you want but, it would be slow and ghostly sounding.) and you can covert any language you know into Sign Language.

 Beheaded Ones are driven by some unexplainable force to stop injustice in its tracks. They can have any Good alignment or be lawful neutral.

A Beheaded One's size may vary depending on which body they are possessing, But they can only be in any body that has a size of small or medium. (See Inhabit trait for details)

A Beheaded One's speed can vary based on the size the the body they've inhabited. A Beheaded One's speed is 30 feet in a medium sized body and 25 feet in a small sized body. 

Being a Beheaded One, you can see in every direction at once, though you still have the normal sight range of a human you can be suprised due to being aware of your surroundings at all times.

Since you are in a dead body, you do not need to eat, drink, or sleep.

You have proficiency in all one handed simple weapons.

As an action, you may launch your true form out of the top of of body you are in. When you do so, the smoke form on top of your body disappears. This form looks like a pile of moving plant matter. This form is connected to your neck by a cord of the same material. While you are in this form, you have a walking and climbing speed of 25 feet, and you may only move 50 feet away from the body, or be suddenly returned to the body. You may also latch onto another creature in this form. If you do so, you may cause that creature to take 1d6 acid damage at the start of each of its turns. You may move your body when latched onto someone. When you are reduced to 0 hit points, you become your true form, except not attached to the body, and able to move as afar as you want. You must inhabit another body (see Inhabit trait) or be submerged in blood by your next turn, or make the death throws. Consider asking a teammate to carry a container of blood for you to submerge in. Your true form's size is Small.

You are able to posses the corpse of a headless body using your true form to enter the space where their head was, whether you are attached to your body or not. When you do so, you retain your Class(es,) levels, features, spells and feats, but you must retrieve your items from your body. Also, the smoke form appears in place of the new body's head. You may only possess humanoids of Small or Medium size.

You have the ability to summon a ball of magical energy that resembles a cell. Doing so takes 1 bonus action. You may use a Cell as a ranged weapon. On a hit, the target takes 1d6 radiant damage(# of die increase based on level). Once you use a Cell this way, you may not do so on your next turn. Additionally, you may consume a cell. Doing so gives you a +1 on your next roll. Once you use a Cell this way, you may not do so again until you finish a short or long rest.