Urstel, The Black Blade

Assassinate. You have advantage on attack rolls against any creature that hasn’t taken a turn in the combat yet. In addition, any hit you score against a surprised creature is a critical hit.

Martial Adept. You have two maneuvers at your disposal. If a maneuver requires your target to make a saving throw, the DC is 17. Your Superiority die is a D8.

Mobile. When you use the Dash action, difficult terrain doesn't cost you extra movement. When you make a melee attack against a creature, you don't provoke opportunity attacks from that creature, weather you hit or not. 

Sneak Attack. Once per turn, you can deal an extra 3d6 damage on your weapon attack. You can do this if you have advantage or if your enemy is within 5 ft. of an ally. 
Wails From The Grave. Immediately after you deal your Sneak Attack damage, you can deal 2d6 Necrotic damage to any creature within 30 ft. 

Hand Crossbow. Ranged Weapon Attack: +9 to hit, reach 30(120) ft., 1 target. Hit: (1d10+6) Piercing damage. Target must make a DC 10 CON save or take an additional 9 (3d6) Poison damage.

Throwing Dagger. Ranged Weapon Attack: +9 to hit, reach 20/60 ft., 1 target. Hit: 8 (1d4 + 6) Piercing damage. Target must make a DC 13 CON or become Poisoned.
Infected Sickle. Melee Weapon Attack: +9 to hit, reach 5 ft., 1 target. Hit: 10 (1d8+6) Slashing damage. Target must make a DC 10 CON save or take an additional 18 (6d6) Poison damage.
Disarming Attack. Maneuver Weapon Attack: +9 to hit, reach 5 ft., 1 target. Hit: 10 (1d8+6) Slashing damage. You expend one superiority die to add it to the damage and to disarm the target if it fails a DC 17 STR save. 

Cunning Action. You can take a bonus action on each turn to take the Dash, Disengage, or Hide action. 

Feinting Attack. You can expend one superiority die and use a bonus action on your turn to feint, choosing one creature within 5 feet of you as your target. You have advantage on your next attack roll against that creature this turn. If that attack hits, add the superiority die to the attack’s damage roll.

Uncanny Dodge. When an attacker that you can see hits you with an attack, you can use your reaction to halve the attack's damage against you. 

Law of Spiders. When an ally within 60 ft. of you falls to zero hit points, Urstel can use their reaction to take (X) amount of Necrotic damage (ignoring Resistance and Immunity) and gift their ally temporary hit points equal to the damage taken.