Taken from Japanese mythology by way of Nioh, suitable for an Oriental Adventure campaign.
BIWA BOKU-BOKU
Small undead (yokai), chaotic evil
Spellcasting. The yokai is a 4th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 12, +4 to hit with spell attacks). Any bard spells the yokai has prepared only require somatic components to cast. It has the following bard spells prepared:
- Cantrips (at will): friends, mage hand, vicious mockery
- 1st level (4 slots): charm person, healing word, heroism, sleep, thunderwave
- 2nd level (3 slots): invisibility, shatter
Ethereal Jaunt. As a bonus action, the yokai can magically shift from the Material Plane to the Ethereal Plane, or vice versa. While on the ethereal plane it gains a speed of 30 ft.
Ethereal Sight. The yokai can see 60 feet into the Ethereal Plane when she is on the Material Plane, and vice versa.
Taunt (2/Day). The yokai can use a bonus action on its turn to target one creature within 30 feet of it. If the target can hear the yokai, the target must succeed on a DC 12 Charisma saving throw or have disadvantage on ability checks, attack rolls, and saving throws until the start of the yokai’s next turn.
ACTIONS
Bitter Summons. The yokai magically summons an undead of CR 3 or lower or an oni-bi* with a 50/50 chance of either. The summoned creature appears in an unoccupied space within 60 feet of its summoner and acts as an ally of its summoner. It remains for 10 minutes, until it or its summoner dies, or until its summoner dismisses it as an action.
* Use any CR 2 or less elemental creatureto represent the oni-bi.
DESCRIPTION
Pronounced “BEE-wa BOH-koo BOH-koo.” A yokai taking the form of a monk playing a biwa lute. The biwa is the yokai itself; the “monk” is simply a reflection of Hoichi, the biwa player whose unwise dealings with restless Heike warrior spirits cost him both his ears. Lures intruders deeper into places of evil with its eerie melodies.
Heroes will hear this yokai well before they see it.