By Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging
encounters against Oni
Note: This has been prepared utilizing only the 5E Core Rules. The Oni can be found in the Monster Manual page 239.
The Oni are fearsome bogeymen that haunt the nightmares of children and adults alike. While the question remains: which came first, the Oni or the Fear? The simple fact is that the Oni are now very real and always hungry.
The Oni are nocturnal hunters, hiding its true form by means of magic and often attempting to befriend the parents, relatives, and friends of its chosen victim. It may even attempt to endear itself to the victim itself.
Obviously, this deception requires the Oni to be able to transform themselves into a human or human-like creature to enable it to walk freely among the people. This form can be as small as a Halfling or Kobold to as large as a Dragonborn or even a Goliath.
They usually pose as travelling tradesfolk or simple travelers, often using the ruse of trading a fair day’s labor for a place in a warm barn and a hot meal. Once accepted however tentatively into a household, the Oni will use that trust to devastate and destroy, mainly for the simple pleasure it derives from pain it inflicts.
The Oni are sometimes called the Ogre Magi, or more literally Magic Ogres, because of their large Ogre-like size and their magical ability. Highly intelligent these creatures will often form alliances with other evil creatures to penetrate communities and especially castles or fortifications as a living “trojan horse”.
Step 1) Let’s Review what we know about the Oni:
Physically the Oni are amazingly strong (+4) and exceptionally tough (+3), Their dexterity slightly above average and unremarkable.
Mentally the Oni are exceptionally intelligent (+2), have strong wills (+1) and have forceful, persuasive personalities (+2).
Oni wear chainmail, and thanks to their unique physiology they do not have to remove it to rest comfortably.
Oni can move on the ground or fly at the same speed (30 feet).
Oni are very resistant to being affected by magics and physical attacks having proficient saving throws in Dex (+3), Con (+6), Wisdom (+4), and Charisma (+5).
Oni have a natural ability and perhaps some ‘hand-me-down’ training in Arcana (+5), Deception (+8), and Perception (+4).
Oni have Darkvision (60-foot) and a Passive Perception of 14.
The Oni can speak Common and the language of Giants.
The Oni are natural spellcasters (Charisma Save DC 13). They can cast Darkness and Invisibility at will, and can cast Charm Person, Cone of Cold, Gaseous Form and Sleep once each day.
The Oni regenerate, restoring 10 hit points at the start of its turn, provided it has at least one hit point.
Oni are natural shape-changers and can transform themselves into any type of humanoid creature from small to giant sized, any equipment carried transforms with them and is sized correctly for the new form.
Step 2) Determine the probable Strategy.
When an Oni is on its own, it seeks only to cause mayhem and disruption. Interestingly enough, humanoid settlements are not immune to attacks, the Oni will happy tear apart a group of Orcs, Goblins, Hobgoblins or Gnolls.
When an ally of other evil forces, the Oni are most often used as a “Trojan Horse”, using their shape change ability to enter the settlement in disguise, then charming or putting to sleep persons who stand between it and the gate.
Once the settlement is breeched the Oni will revert to its primary desire: destruction and mayhem.
Step 3) Determine Tactics
Armed with their glaive or even just their claws. The Oni will push forward in combat isolating a single foe whenever possible. The initial attack will be from invisibility, granting it advantage.
When using the Glaive, it will be wielded two handed. Taking advantage of both the 10-foot reach and the much higher damage potential. When the foes are weak, the claws are a far more satisfying weapon to these creatures.
Do not forget that as the only can fly, they can easily move about the battlefield, and will often utilize their Glaive from high and out of reach of their foes. As this tactic is significantly impaired by missile weapon wielders and spell-users, these are primary targets for the Oni.
If there are many strong combatants, the Oni will utilize its Cone of Cold to weaken them. Any ‘statues’ created can be used as throwing weapons (19 Strength).
After it kills one foe, the Oni will utilize Darkness to regain invisibility and the ability to attack from hiding once more. Darkness may not be necessary, as the nocturnal nature of the Oni may provide the night sky for concealment.
The Oni are disciplined fighters and will coordinate their attacks and strategy with their evil allies.
The Oni are no stranger to the utility provided by flaming oil and poison. They will often use burning oil in open areas of conflict to disturb and disrupt the dark vision of foes.
If the Oni feel truly threatened by a determined foe, then it will utilize its ability to fly or its Gaseous Form to affect its escape.
Step 4) DM Tips and Observations:
Armor Class 16 is way too low. Combatants fighting such would average a +6 to hit, meaning that they would hit on a 10+. Add in “Chainmail”, even the picture in the MM shows different. Natural Armor, AC: 20 is a more reasonable description of the abilities.
Anyone who has read many of these essays knows that I dislike half measures. Make the Strength 18 and the Charisma 16.
I would vary the speed of the Oni based on the size of the form it chooses to portray: Small 25, Medium 30, Large 40, or Huge 50.
I like the invisibility and the attack from hiding, but there needs to be some UMP to that attack. I would suggest that when attacking from INVISIBLE, the Oni gains Sneak Attack +3d6 damage.
I would like to add the cantrip Prestidigitation to the ‘At Will’ Spell list of the Oni. This would provide the ability to create distractions and of course to light the dropped burning oil.