Assassinate. During its first turn, the ninja has advantage on attack rolls against any creature that hasn't taken a turn. Any hit the ninja scores against a surprised creature is a critical hit.

Evasion. If the ninja is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, the ninja instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Sneak Attack. Once per turn, the ninja deals an extra 14 (4d6) 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 ninja that isn't incapacitated and the ninja doesn't have disadvantage on the attack roll.

Shadow Arts. The ninja's  innate spellcasting ability is Wisdom (spell save DC 14). The ninja can replicate the following spells using Kuji-in, requiring no material components:

At will: minor illusion

1/day each: darkness, darkvision, pass without trace, silence

Shadow Step. When the ninja is in dim light or darkness, the ninja can teleport up to 30 feet to an unoccupied space you can see that is also in dim light or darkness as a bonus action.

Multiattack. The ninja makes two ninjatō attacks or throws two shuriken.

Ninjatō. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) piercing damage, and the target must make a DC 13 Constitution saving throw, taking 17 (5d6) poison damage on a failed save, or half as much damage on a successful one.

Shuriken. Ranged Weapon Attack: +7 to hit, range 20/60 ft., one target. Hit: 6 (1d4 + 4) piercing damage, and the target must make a DC 13 Constitution saving throw, taking 17 (5d6) poison damage on a failed save, or half as much damage on a successful one.