I am currently running an Oriental Adventures (OA) campaign called The Divine Heir and the Jade Regent loosely based around the Pathfinder Adventure Path the Jade Regent with strong influences from Sekiro. The first adventure is called The Ashina Legacy and is essentially the The Brinewall Legacy set in and completely converted to an OA setting.
I had to rewrite the adventure intro and re-theme the monsters but it worked well. Here is the flowchart of the adventure (and campaign).
Tsutamu is a dragon clan (and armoured) undead/skeletal samurai. Inspired by the original from mythology and Legend of Five Rings. This was a do or die fight for level 1 characters as he was supported by skeletal samurais (standard skeletons retimed with Japanese armor and weapons). And his poison breath was particularly dangerous.
Just a note on language. Though I still use Common its the Common of the Orient so not interchangeable with the standard D&D language.
TSUTAMU the HYAKUHEI
Medium undead (yokai), lawful evil
Armor Class 16 (ashigaru armor)
Hit Points 45 (6d8 + 18)
Speed 20 ft.
STR DEX CON INT WIS CHA
18 (+4)12 (+1)17 (+3)6 (-2) 9 (-1) 10 (+0)
Damage Resistances necrotic; bludgeoning, piercing, and slashing from nonmagical attacks that are not crystal
Damage Immunities cold, poison
Condition Immunities exhaustion, frightened, poisoned, unconscious
Senses darkvision60 ft., passive Perception 9
Challenge 3 (700 XP)
Command Skeletons. Tsutamu has a unique bond to the skeletons found in Omikura Swamp. He can command their actions as a free action via telepathy as long as they’re within line of sight. If Tsutamu is destroyed, the other skeletons immediately collapse to the ground as well, for it is the samurai’s will that keeps them animated.
Martial Fury. As a bonus action, Tsutamu can make one weapon attack. If he does so, attack rolls against it have advantage until the start of its next turn.
Order. Tsutamu’s order is ronin. Whenever Tsutamu is the target of a challenge by another samurai and he issues a challenge against that character in return, he receives a +1 bonus on attack rolls made against the target of his challenge and a +1 bonus to AC against attacks made by the target of his challenge.
Resolve (1/Day). Tsutamu has advantage on Constitution and Wisdom saving throws.
Self-Reliant. Whenever Tsutamu fails a Wisdom save against an effect with a duration greater than 1 round, he can attempt another saving throw at the end of the second round of the effect. If he makes this saving throw, it has the same effect as if he had made the original save.
Fear Aura. Anyone within 5ft. of a hyakuhei is affected by the aura of fear that surrounds it. Anyone within the area of effect must make a DC 10 Wisdom saving throw or freeze in place frightened.
Multiattack. Tsutamu makes a whispering shrike and tearing claw attack.
Whispering Shrike. Melee Weapon Attack:+7 to hit, reach 5 ft., one target.
Hit: 8 (1d6 + 5) slashing damage.
Tearing Claw. Melee Weapon Attack:+6 to hit, reach 5 ft., one target.
Hit: 7 (1d6 + 4) slashing damage.
Daikyu. Ranged Weapon Attack:+3 to hit, range 150/600 ft., one target.
Hit: 5 (1d8 + 1) piercing damage.
Poison Breath (1/Day). Tsutamu exhales shadowland tainted gas in a 15-foot cone. Each creature in that area must make a DC 11 Constitution saving throw, taking 14 (4d6) poison damage on a failed save, or half as much damage on a successful one.
Deflect. Tsutamu may deflect an attack that hits and damages him. He rolls 1d10+1 and subtracts that from the damage taken. If he fully cancels the damage from a melee weapon attack, he may make a counterattack as well with whispering shrike.