Warforged Headhunter

Efficient Killer. Whenever the warforged reduces a creature to 0 hit points with a weapon attack, that target dies.

Warforged Resilience. The warforged has advantage on saving throws against being poisoned and it is immune to disease. Magic can't put it to sleep.

Ambusher. The warforged has advantage on Initiative checks, and it has advantage on any attack roll made against a creature that hasn't acted in the current initiative order yet.

Sneak Attack (1/Turn). The warforged deals an extra 10 (3d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of the warforged that isn't incapacitated and the warforged doesn't have disadvantage on the attack roll.

Multiattack. The warforged makes three weapon attacks.

Spear. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 8 (1d8 + 4) piercing damage. If the target is marked, it takes an additional 5 (2d4) piercing damage.

Heavy Crossbow. Ranged Weapon Attack: +7 to hit, range 100/400 ft., one target. Hit: 9 (1d10 + 4) piercing damage. If the target is marked, it takes an additional 5 (2d4) piercing damage.

Execute Quarry (Recharge 6). The warforged targets one marked creature it can see within range of one of its weapons, and makes an attack with that weapon. On a hit, the affected creature must make a DC 15 Constitution saving throw taking double damage from the attack. on a successful saving throw, the target only takes 10 additional damage. If the damage dealt from this attack reduces the target to 20 hit points or less, it dies.

Stealthy. The warforged takes the Hide action.

Mark Quarry. The warforged designates one creature it can see within 120 feet of it as a priority target until it is slain, marking that creature. While so marked, the warforged has advantage on the first attack it makes against that creature on its turn, the creature can't benefit from half or three-quarters cover against the warforged's attacks, and warforged's critical threshold is reduced by 1 against the marked creature. The warforged can only have one creature marked in this way at a time, though it can changed its designated target using a subsequent bonus action.

Uncanny Dodge. As a reaction to taking damage from an attack, the warforged halves the incoming damage.