The Tengu, large and powerful, is shown to have avian-like features, wears a demon mask, and has black feathers.
When in full control over Howard's body, the Tengu has orange-brown feathers with a blue and purple chest and blue marks on its feathers. Its eyes are glowing red, and its beak has small jagged teeth. On its head, it has a crest resembling Howard's hairstyle, and it can use the ends of its wings as large hands.
Around 800 years ago, the First Ninja and the Tengu fought, but the Tengu was too powerful to destroy. Once the Ninja figured out its ultimate source of power, its feathers, he defeated and trapped it in a sacred stone called the Eye of Eternities. Weaving its feathers into the Ninja Mask gave the Ninja Suit powers, but also forever linked the Ninja and the Tengu. Afterwards, the Sorcerer wanted possession of the stone, but the First Ninja used it to trap him underground instead. Currently, the stone is on the floor of the school lobby, keeping the Sorcerer trapped underground, and it can only be released at the hand of the Ninja.
The Tengu can take over a human body and eventually gain control of it. At first, when the Tengu possesses Howard in "Evil Spirit Week", Howard's eyes occasionally flash red, and feathers begin to grow out of his neck. Over time, he starts acting like a bird without control, like squawking and flapping his arms like wings. He gets exhausted until the Tengu takes complete control over him, which causes him to fully transform into a giant bird. When possessing another body, many of the person's physical features remain, like Howard's hairstyle and hair color.
The time it takes for the Tengu to possess someone varies, from a few seconds to a couple of hours. However, the Tengu seems to desire the control, and usually possesses the most available and closest victim.
The Tengu, while possessing Howard and being controlled by Randy, can use its wings, whether normally or as fists, and feet to fight off foes.
The Tengu is connected with the Ninja, meaning they share the same strengths and weaknesses. If the Ninja suffers an injury, the Tengu suffers the same injury as well. When Randy realized this, he hurt himself in order to force the Tengu to leave Howard's body. Later, he used this connection to control the movements of Howard when he was possessed by the Tengu again. To recapture the Tengu into the stone in both instances, he burned the mask.
- Tengus exist in Japanese folklore and are characterized by their avian and humanized features.
- The Eye of Eternity, the stone the Tengu is trapped in, was also the stone that the sunlight bounced off of that lead Randy and Howard to the Sorcerer's Key in "Randy Cunningham and the Sorcerer's Key".
- In the center of the calendar in "Randy Cunningham and the Sorcerer's Key", the Tengu's face can be seen.
- When Randy absorbs the power of the Tengu, he is allowed to go into Ninja Rage and perform a move called the Ninja Tengu Fireball.
- The Tengu is quite similar in design to Aku from Samurai Jack.
- It is also quite similar in design to Ho-Oh from Pokemon.
- The First Ninja is able to perform a fire move similar to the Tengu Fire Ball yet it looks like a dragon and his suit doesn't change color. It is unknown if this power is also linked to the Tengu.