The creature exhibits signs of instinctive cunning rather than rational intelligence. Ao Oni acts with aggression towards perceived intruders. In such situations the demon's actions indicate a degree of creativity, but shows little application of that intellect outside of chasing trespasser off. It is notable that Ao Oni doesn't follow people outside of it's lair. It is unknown if this is because it cannot or because it doesn't want to.
Infrared Vision - Ao Oni eyesight can see infrared spectrum, which means it can see body heat.
Death Transformation - When Ao Oni's actions result in death, humans or even animals turn into more of it's kind. These new Onis only difference from the original Ao Oni is their hair, which remains the same as the person it was formed from.
Shapeshifting - The creature has the ability to transform itself to resemble a human more accurately. Onis that have been created from it's victims can transform back to their human form.
Mimicry - There are instances where Ao Oni has the ability to mimic speech to lure and trick people.
Aside from the Ao Oni and those it transforms, there are a number of irregular Onis. Each resembles a different version of the original and are locked in a cage in what is known as the Oni Room. These are the:
- Blockman Oni - This is a square-shaped oni that moves quicker than the regular Ao Oni. When it spots its victim, it pauses for a moment then charges at it with abnormal speed. In Version 6.23, it became an official enemy, replacing the Roach Oni of Version 5.2.
- Hunchback Oni - The Hunchback Oni is a normal oni, though its back is hunched over, and it constantly has it's teeth bared.
- Hulk Oni - Known to fans of the game as "Squato," this oni is a large, muscled oni that bangs the floor for no apparent reason. Because of its size, it moves slowly in most cases. It is the largest of the onis. This Oni appeared as a secondary antagonist in Version 3, as well as many fan-made games.
- Deformed Oni - This oni resembles the regular Oni, though the oni itself is completely warped, hence the name.
- Blob Oni - Also known as the "Eye-see Oni", this oni is irregular. It looks like an amorphous mass with many eyes on it. The Blob Oni is relatively slow and sluggish.
- Encephalo Oni - This oni mutation is the head of the regular oni but lacks a mouth and has many tentacles. It bears resemblance to a jellyfish.
- Caterpillar Oni - This oni is also a sluggish type of Oni. It looks like a caterpillar with its head up. It has 5 eyes on each side and many, tiny legs.
- Flying Oni - This oni has spike-like protrusions from its head and floats back and forth without any other movement, Its nickname is called "Niji Oni"
- Clock Oni - The oni resembles a clock with thorns, as if exploding, or a stalactite. It levitates while staying affixed to its position, one of the thorns stretching and shrinking continuously. It is possible that the Clock Oni is merely the Flying Oni looking straight ahead.
- Tall Oni - A much taller version of the regular Oni. Other than it's height, there appears to be no difference between the two.
- Toothed Oni - A perfect copy of the original Oni, the only thing that makes the Toothed Oni irregular is the expression it wears. Whilst the true Ao Oni has a bemused expression, the Toothed Oni seems to be enraged, baring it's teeth in a similar manner to the Hunched Oni.
- Roach Oni - Appearing in Version 5.2 as a secondary antagonist, this Oni is similar to the Blockman. In appearance, it looks like a giant blue cockroach (hence the name) with an eye on the side of it's body.