Aohada

Compassionate Heart. The Oni can bless a creature with temporary hit points when they take the Help action. When they do, they use up a hit die and grant 1d10+7 temporary hit points to the target. They can use this trait a number of times equal to their proficiency bonus.

Innate Spellcasting. The Oni's innate spellcasting ability is Charisma (spell save DC 14). The Oni can innately cast the following spells, requiring no material components:

At Will: Darkness, Invisibility

1/day each: Charm Person, Cone of Cold, Gaseous Form, Sleep

Magic Resistance. The oni has advantage on all saving throws against the poisoned condition and all spells or other magical effects.

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

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

Multiattack. The oni makes two attacks, either with its claws or its naginata.

Claw. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 8 (1d8 + 2) slashing damage.

Crunching Maw. Melee Weapon Attack:  +6 to hit, reach 5 ft., one target. Hit: 3 (1d4 + 2) piercing damage.

Naginata. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 9 (1d10+2) slashing damage.

Change Shape. The oni can magically polymorph into a Small or Medium humanoid, into a Large Giant, or back into its natural form. Other than its size, its statistics are the same in each form. The only equipment that is transformed is its naginata, which shrinks so that it can be wielded in humanoid form. If the oni dies, it reverts to its true form, and its naginata reverts to its normal size.

Reactions

Savage Bite. When you take damage from a creature within 5 feet of you, you can magically enlarge your jaw and lash out with a vicious bite. Use your Crunching Maw ability against that creature. This attack can score a critical hit on a roll of 18, 19, or 20.