How to Play an Oni like a Living Nightmare

A halfling paladin sat in bed, gazing out a dusty old window that looked out onto the moors. He kept his sword by his bed tonight, as he had the past three nights in this old manse, even though his three traveling companions were in other beds nearby. It was well past midnight, but still he sat awake, staring apprehensively out the window. He jolted under his sheets and whipped his head towards the door to his party’s communal room. The door had opened with long, whining creak. His chest tightened and his pulse quickened. He reached for his sword. The leather wrapped around its pommel was cool in his grip as he stared unflinchingly towards the darkness of the hall beyond. Yet even as he steeled himself for whatever terror he knew lurked within this old house, he felt a memory from his childhood tug at his mind. A nursery rhyme. A grim one, the kind that parents sing to their children to scare them into behaving. Without thinking, he sung the words under his breath. Lock the door, blow out the light; The hungry oni haunts the night. He stood, and the chill of the floor rushed up through his bare feet. He strode towards the door, past the sleeping human wizard, past the elven barbarian, deep in a trance, and past the snoring halfling cleric, his friend from the old country. He stopped at the threshold of the dark hallway and stared into the abyss. Hide and tremble, little one; The oni wants to have some fun. His grip on the blade tightened until his knuckles were white and his small hand trembled. He took a deep breath and plunged into the hall. Only the faint glow of the moonlight through the windows lit his path. It struck the suits of armor that lined the hall and cast spectral shadows across the wall. Hear it scratching on the door; See its shadow cross the floor. He stopped dead in the middle of the hallway, and fear and dawning realization clutched his heart. He turned back toward the door to his room, praying to Yondalla not to see what he thought he would see. The door, slightly ajar, was scored by deep claw marks. Within, a long shadow crept across the floor towards his friends’ beds. And as he wheeled and ran back towards his room, he realized—he had never been the one singing. The sun won’t rise for quite a while; Till then, beware the oni’s smile.

There are few creatures in Dungeons & Dragons as criminally underappreciated as the oni. It is one of D&D’s oldest monsters, first appearing as the “ogre mage” in Supplement 1: Greyhawk (1975) alongside the beholder and the mind flayer. The oni is Dungeons & Dragons designer Mike Mearls’ favorite monster, and it is a creature that successfully marries interesting gameplay and compelling narrative. It deserves a spot in the D&D hall of fame just like its better-remembered contemporaries, and it deserves a place in your home game because, when played well, it can be the star of a session your players will talk about for years to come.

The “D&D” Oni

An oni is a creature from Japanese folklore, but like all mythological creatures that D&D borrows, the oni in the Monster Manual bears only a passing resemblance to its Japanese counterpart. We’ll discuss how to make your oni more like that which appears in Japanese legends later in this article. It is worth noting, however, that even in the oni’s first appearance as the “ogre mage” in Supplement 1: Greyhawk, it was specifically called a Japanese ogre, noting “[Ogre Magi] are properly Japanese Ogres, far more powerful than their Western cousins!”

These days, the oni has been recast as a bogeyman that loves to feast on human infants. They use dark magic to disguise themselves as humanoids or as giants to stalk their prey, then strike at night. No longer great shamans of ogrekind, they are now only distantly related to true ogres. This change of taxonomy may be jarring to those who grew up loving the ogre mage (Mike Mearls often accidentally calls the oni an ogre mage in interviews), but it makes perfect sense to D&D newcomers, and even just newcomers to ogre magi in general, and that’s because playing an oni is nothing like playing an ogre.

Art by Greg Bell for Supplement 1: Greyhawk by Gary Gygax and Rob Kuntz

In Combat: Oni, Night Terror

Oni may be Giant-type monsters, but save for their size and troll-like Regeneration powers, they are nothing like the other giants in the Monster Manual. Oni do not fight like ogres, using brute force to slaughter the small folk. They are ghastly creatures that lure creatures into a web of arcane deceit, only to strike from the shadows when their prey is at their weakest. Oni are excellent monsters to keep in your back pocket as a Dungeon Master, because their impressive mix of magic and raw power make them a versatile foe for nearly any occasion.

The story details in the Monster Manual suggest that oni are loners, or at least act as lone-wolf assassins for masters that promise them magical power in return. They rarely fight fair, instead using their magic to lurk in the shadows like a specter, and employing fear and psychological tactics to weaken their foes before striking. If you use the oni’s magic cleverly, you may be able to fool your players with a deadly surprise attack, and then escape without taking even a single hit. An oni can easily punch above its weight class and bring ruin upon an unprepared party. If your players hate feeling powerless, you should wait until their characters are at least 7th level before you confront them with an oni. But if they enjoy the pulse-pounding thrill of being stalked like teenagers in a slasher film, the oni delivers in spades. Its combat traits are a perfect match for its spooky lore.

An Oni’s Traits

About half of an oni’s traits are focused on allowing it to strike from surprise, and from any angle—and then escaping to fight another day. The other half are geared towards utterly slaughtering its victims in those precious few seconds it has before it flees, invisible, into the night.

Defenses. Judging by the monster-building guidelines in the Dungeon Master’s Guide, the oni’s defenses are supbar, but workable. It can probably last for one or two rounds in a straight-up fight thanks to its slightly above-average Armor Class, but it simply doesn’t have the hit points to survive a straight-up slugfest. Its Regeneration trait improves its survivability a little bit, though it only gives the oni about 20-30 extra hit points in an average combat encounter.

Movement. The oni’s 30-foot flying speed is an unbelievably powerful tool, especially because it can cast invisibility at will. (The fact that it possesses an innate flying speed is significant, since both fly and invisibility require concentration. An invisible, flying oni can move with impunity. If even invisibility isn’t enough, the oni can also cast gaseous form once per day. This spell could be used as a way to sneak into a well-guarded compound by traveling under closed doors or barred windows, but it’s most useful as a panic button that the oni can use to retreat in dire circumstances. It doesn’t make it immune to all damage, and it reduces the oni’s flying speed to 10 feet, so you must have the presence of mind to use an action to cast it before the fight goes south.

Subterfuge. An oni can use its Change Shape trait to polymorph into a Small or Medium humanoid or any Large giant—such as an ogre, a cyclops, or a troll. Imagine the players’ surprise when the tiny halfling they thought was their friend turns out to be a hulking oni!

Innate Spellcasting. An oni’s power is largely derived from its spells. It can cast invisibility and darkness at will, though keep in mind that it cannot cast them both at the same time, as they both require concentration. Since invisibility is a superior defensive spell in most situations, an oni should use darkness offensively to blind opponents. Darkness’s major defensive advantage over invisibility is that the darkness persists after attacking or casting a spell, whereas invisibility ends immediately after attacking or casting. Even though you can cast it at will, one round of visibility could be enough for the party to dogpile on the oni and tear it apart.

An oni has four spells that it can use once per day, each: charm person, cone of cold, gaseous form, and sleep. Cone of cold is the true powerhouse spell here, and an oni should almost always begin its attack by casting cone of cold from stealth, if it can catch the entire party in the blast—and its 60-foot range means that an oni can use it even when flying out of reach of melee fighters. Charm person can be useful in social situations, especially when the oni has taken on another form using its Change Shape trait. Sleep is generally too weak to be an effective spell, but casting it right after catching the entire party in a cone of cold could be deadly.

Physical Attacks. One of the tell-tale signs of an oni is the wicked glaive it carries. Beware charming halflings wielding wicked glaives. An oni’s physical attacks are quite weak compared to other CR 7 monsters, and should only be used after its targets have been weakened by a cone of cold. You must exercise restraint; no self-respecting oni should get caught in an extended melee. Hit fast, use the glaive to deal a finishing blow or two if necessary, and then flee.

An oni’s physical weapons are magical, so you can overcome resistance to nonmagical weapons, which is worth something.

An Oni’s Tactics

As I said in How to Play a Mind Flayer like an Eldritch Horror, “The first rule of horror movies is that the monster is always less scary once you see it.” The oni wants to strike fear into the hearts of its victims by being invisible and untouchable. Fortunately, unlike a mind flayer, the oni still has some staying power once it comes out of hiding.

An oni rarely wants to strike from total surprise. Its modus operandi is to stalk its prey like a horror movie slasher, taunting them from afar so that its targets are thrown off their game. Perhaps the oni makes its presence known the players at the beginning of a dungeon, pops into every single fight within that dungeon and delivers a few cheap shots, and then turns invisible and hides as soon as it is reduced to about half of its maximum hit points. Any incidental wounds it sustains will be fully healed by its Regeneration trait before the next fight. After harrowing the entire dungeon like this, the characters must finally face the oni as the boss, still at full power.

If the characters ever decide enough is enough and cast dispel magic to nix its invisibility, then it strikes with its full force, casting cone of cold to annihilate as many of its foes as possible in a single stroke.

Truly evil DMs can use the oni to interrupt a party’s short and long rests, preventing them from ever recovering while within the dungeon. This might be too hardball for DMs with new players, but if you know your players can handle it, this will show them that nowhere is safe when you are being stalked by an oni.

Your tactics may vary based on the needs of your campaign, but an effective and powerful tactical loop for an oni is:

Stay in oni form while fighting unless you have a good reason not to; your Large size improves the damage of your glaive.

Begin combat flying, and never stop unless absolutely necessary. Always end your turn at least 20 feet off the ground. Fortunately, your glaive’s 10-foot reach will likely prevent you from ever provoking an opportunity attack from retreating into the air after a melee attack.

Begin combat invisible. If you end your invisibility for any reason, you can try to fake out your enemies by moving 10 feet in one direction, casting invisibility, and then moving 20 feet in another direction. The characters can always attack invisible creatures at disadvantage, but if they target a space that doesn’t contain a creature, then they simply have no chance of hitting at all!

If you’re just harassing the party and plan to flee, attack with your glaive from 10 feet away while invisible, then flee. Turn invisible using your action on your next turn, and repeat until you have about half your maximum hit points, then escape combat while invisible.

If you’re forced into a life-or-death situation, start combat by hitting the entire party with cone of cold, using your flight to get a good angle. If you think the party is severely wounded, cast sleep on your next turn as a follow-up. Turn invisible as often as possible.

If you're reduced to ¼ of your maximum hit points and can escape through a small crack, use gaseous form to try to escape so you can live to fight another day.

Alternate Oni

This article wouldn’t be complete without some discussion of the actual Japanese oni, as well as some ways to make the oni in the Monster Manual an even more serious threat.

An oni’s powers in D&D are reasonably faithful to the oni of Japanese folklore. Japanese oni are evil spirits that manifest as monstrous horned ogres. They are not necessarily evil, but are typically cruel and menacing. Traditionally, oni do not wield a glaive (naginata), but wield an iron club known as a kanabō. It would be perfectly reasonable to replace a D&D oni’s glaive with a greatclub, such as the kanabo greatclub I created for Kobold Press's Beyond Damage Dice series.

One strange inconsistency in the oni’s stats as presented in the Monster Manual is that it wears chain mail. Its art does not depict it in chain mail, but this poses a more significant problem than inconsistent art. When an oni uses its Change Shape feature, “the only equipment that is transformed is its glaive, which shrinks so that it can be wielded in humanoid form.” If the rules are strictly followed here, its chain mail is unaffected by this trait, leaving it defenseless after it changes shape. An easy way to house rule this problem away is to simply give it “Armor Class 16 (natural armor),” resolving both the mismatched art and the problematic rule.

Since oni are supposed to be stealthy stalkers despite their size, I would also give it Stealth proficiency instead of Perception proficiency, giving it a bonus to Dexterity (Stealth) checks of +3.

If you want to make your oni more powerful, recall that they are always in search of new magical items. According to the Monster Manual, “An oni serves a master if doing so proves lucrative or provides it with a luxurious, well-defended home. Oni covet magic, and they work for evil wizards and hags in exchange for useful magic items.” An oni with a magic item that lets it attack from range at will, like a wand of magic missiles, makes it an even more dangerous foe. A cloak of displacement is also perfectly in-character, and gives it a little more staying power in combat.

Having Fun Playing an Oni

D&D is always about having fun, and as a DM you are granted the challenging task of helping your players enjoy the game while also having a good time yourself. Some players love horror or suspense games, and will love the thrill of being stalked by an oni. Others will get stressed out by it, or just get annoyed by trying to fight an elusive foe. Pay attention to the messages your players are sending you, and be prepared to dial it back for future games if they had a bad time. It's probably best not to spring this kind of game on first-time players, unless everyone at the table is a big horror buff.

Try to find the right balance between stress and excitement. It will take practice, so don’t expect to get it right the very first time. Good luck, and happy nightmares!

James Haeck is the lead writer for D&D Beyond, the co-author of the Critical Role Tal'Dorei Campaign Setting, and a freelance writer for Wizards of the Coast, the D&D Adventurers League, and Kobold Press. He lives in Seattle, Washington with his partner Hannah and his two prowling demons, Mei and Marzipan. You can usually find him wasting time on Twitter at @jamesjhaeck.