Score upgrades. +2 Dex and -2 Con, also choose between +1 Cha or +2 Int.

Keen ears. You have blindsight for 30ft and have advantage on perception checks using hearing.

Dark vision. You can see up to 60ft in complete darkness and you can see in color. 

Vulnerability. Fire and radiant damage.

Resistance. Poison damage.

Sunlight sensitivity. You have disadvantage on perception checks made using eye sight while in direct sunlight or bright light.

Sneaky. You have advantage on stealth checks.

Hooves. Your unarmed strikes deal 1d4 + Str bludgeoning damage. You are considered proficient with these attacks. Should the player choose their Thestral can walk upright on two legs like a biped, however can only walk at half speed.

Size. You are medium sized at about 4ft tall. You weight between 60 -100 pounds.

Wings. You can fly a distance equal to your ground movement speed. You can use your wings almost like hands in order to do very fine tasks. You may also wield weapons using your wings however you cannot fly if you are holding an item that is larger than a light weapon.

Tail. Your tail can be used to wrap around objects in order to hang upside down. You cannot do fine tasks using this feature though. 

Shadow Step. Once per 8hrs as an bonus action you may choose to magically turn into a shadowy mist for 1 round making yourself untargetable by most non-magical attacks, you can still be harmed by radiant, fire, cold, thunder, and phychic damage. You can still move around and fly as normal but cannot use other actions or bonus actions until this effect ends. If you are in a dark environment you become invisible. If you are in a environment lit with bright light or sunlight you will take 1d6 radiant damage while using Shadow Step. This effect ends at the end of your next turn.