Living Shadow

shadowfell spy

enveloping darkness

you gain a 300ft dark vision and the ability to see through magical darkness 
and can cast darkness a number of times equal to your proficiency bonus / long rest  

Poisoned Blades

after you hit with an attack to a creature, you can choose to change the damage type of your sneak attack to poison forcing the target to make a con saving throw or become poisoned 

Blinding light in the dark

 you can cast greater invisibility proficiency bonus times per long rest 

while invisible your weapon attacks do 2d8 radiant damage and a con save vs blindness

Shadow form

as a bonus action you can assume shadow form for 10 min

while in this form you can walk on vertical surfaces and ceilings. you gain resistance to damage other than fire, force, psychic and radiant damage but gain vulnerability to fire and radiant damage

you can take this form once per short rest

 

Relentless shadow

When you are reduced to 0 hp you make a con save dc 10 on a success roll your sneak attack dice and regain that many hit points
the dcc increases by 5 for each time they drop to 0hp resetting after a long rest