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

Innate Spellcasting. The oni's innate spellcasting ability is Charisma (spell save DC 15). The oni can innately cast the following spells, requiring no material components:

At will: darkness, detect magic, invisibility

1/day each: charm person, cone of cold, gaseous form, mirror image, mislead, pass without trace, sleep

Magic Weapons. The oni's weapon attacks are magical.

Regeneration. The oni regains 10 hit points at the start of its turn if it has at least 1 hit point.

Shadow Poison. The oni imbues its attacks with magical poison. When it hits with a weapon attack, the attack deals 3 (1d6) poison damage (already included in these attacks).

Sneak Attack (1/Turn). The oni deals an extra 13 (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 oni that isn't incapacitated and the oni doesn't have disadvantage on the attack roll.

Multiattack. The oni makes three attacks: any combination of unarmed strike, dagger, and shortsword attacks. The oni can use its shadow jaunt ability as a bonus action before, between, or after the attacks.

Unarmed Strike. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage (bludgeoning while not in true form) plus 3 (1d6) poison damage and if the oni has a free hand and chooses to use it, the target is also grappled by the oni (escape DC 16).

Dagger. Melee or Ranged Weapon Attack: +9 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 10 (2d4 + 5) piercing damage, or 9 (1d8 + 5) piercing damage in Small or Medium form, plus 3 (1d6) poison damage.

Shortsword. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) piercing damage, or 9 (1d8 + 5) piercing damage in Small or Medium form, plus 3 (1d6) poison damage.

Shadow Jaunt. The oni teleports through its shadow up to 30 feet to an unoccupied space within 5 feet of another creature that it can see. The oni can bring along objects as long as their weight doesn’t exceed what it can carry. It can also bring one creature of its size or smaller that it has grappled who is carrying gear up to its carrying capacity.

Change Shape. The oni magically polymorphs into a Small or Medium humanoid, into a Large giant, or back into its true form. Other than its size, its statistics are the same in each form. The only equipment that is transformed is its daggers and shortsword, which shrink so that they can be wielded in humanoid form. If the oni dies, it reverts to its true form, and its weapons revert to their normal size.