Undead Fortitude. If damage reduces the undead rogue to 0 Hit Points, it makes a Constitution saving throw (DC 5 plus the damage taken) unless the damage is Radiant or from a Critical Hit. On a successful save, the zombie drops to 1 Hit Point instead.

Sneak Attack. Whenever the undead rogue hits with an attack in which it has advantage on or when an ally is within 5' of its target, the undead rogue deals an additional 2d6 damage of the same type of the weapon used to make the attack .

Dagger. Melee Attack Roll: +5, reach 5 ft. Hit: 4 (1d4 + 3) Piercing damage.

Cunning Action. The undead rogue may take the dodge, disengage, or hide action as a bonus action on its turns.

Bonus Attack. The undead rogue may make an additional attack with its offhand dagger if it hasn't used its bonus action for anything else.