Bonegouge assassin

Gloom shroud. As long as the assassin is conscious there is a 10ft sphere of darkness centered on the assassin permanently around them. 

Surprise Attack. If the assassin surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 10 (3d6) damage from the attack.

Darkness of sight. Magical darkness doesn't impede the assassin's sight. 

Multi attack. The assassin  makes 4 attacks, 2 with its bone claws and 2 with its bone darts. 

Bone claw. Melee Weapon Attack: +3 to hit, reach 5 ft., 1 target. Hit: 23 (4d10 + 3) [slashing] damage. 

Bone dart. RangedWeapon Attack: +5 to hit, range 20/60 ft., 1 target. Hit: 13 (2d8 + 5) [piercing] damage and the target must make a dc 15 con save or be poisoned for 1 minute. The the target can remake the save at the end of there turn.