The Mayoi are an artificially created plant-fungi animal hybrid created by Sycorax in Big Hero 6: The Series. Though small and adorable, they can grow to become vicious monsters that Mr. Sparkles can control.
After being accused by Hiro of supplying San Fransokyo with genetically-engineered monsters, Liv Amara set out to improve her public image by taking advantage of her recent alliance with Mr. Sparkle. She created the adorable Mayoi using plant DNA to give it the ability to grow. Once they were unleashed into the city, the citizens were captivated by their cuteness, even surprisingly Go Go. Hiro, on the other hand, was suspicious of them, and immediately suspect that Liv Amara was behind it. Liv Amara also altered Mr. Sparkles' DNA using the Mayoi's plant genes, giving him control of the whole population. By doing this, Mr. Sparkles could take the fall for Liv's schemes, while she made herself look like a hero in stopping him and the Mayoi.
At infancy, the Mayoi are much like puppies and kittens who are playful and love to be fussed over. The only thing they can say is "Mayoi" These traits remain during mid-maturity, but become playfully destructive. When the Mayoi reaches full maturity, they are more predatory and vicious.
At an infancy stage, the Mayoi resemble green fluffy axolotls with stripes and fluffy tails. Their fur is, in actuality, however, fungus. Their ears resemble leaves, resembling more like plants than animals. In further stages of development, they keep mainly the same design until they are fully matured under the control of Mr. Sparkles in which their algae become sharper and its color darkens, and their eyes glow green.
- Mayoi is the Japanese word for "doubt", "hesitation", and "bewilderment". When written in kanji, Mayoi contains 迷い, while "迷" refers to "lost". This could be in reference to their role in presenting Sycorax as an ally to San Fransokyo.