Mushroom allows the user to generate and spread fungus spores from their body.
The spores spread better in an area with high humidity.
Once these spores make contact with a solid surface, they will quickly grow into full-grown mushrooms. The spores can grow from any surface, be it the area, the user's own body, and even other people's bodies.
The mushrooms die after two or three hours.
It's possible to combat the mushrooms with ethanol or some other fungicide.
Kinoko has access to at least two spray bottles that she uses to increase an area's humidity levels, allowing her spores to scatter more easily. She is able to completely cover a terrain with mushrooms in a few minutes through this method, however, in order to prevent her teammates from being affected, they must be sterilized with an antifungal spray first. As a last resort, Kinoko is also capable of growing a mushroom within her opponent's throat, in order to put them in a state of asphyxiation. 
Kinoko's ability works well with Black and Comic, as the former can take advantage of black mushrooms to use as a hiding spot while the latter is able to amplify humidity through the right onomatopoeia, increasing the rate of the mushrooms' growth.
The mushrooms that she has shown to be capable of growing include:
- Black wood cauliflower mushroom (Ionomidotis frondosa)
- Yellow knight mushroom (Tricholoma equestre)
- Enoki mushroom (Flammulina velutipes)
- Inky cap mushroom (Coprinopsis atramentaria)
- Split gill mushroom (Schizophyllum commune)
- ↑ 1.0 1.1 1.2 1.3 1.4 My Hero Academia Manga: Chapter 200.
- ↑ 2.0 2.1 My Hero Academia Manga: Chapter 201.
- Mushroom - Wikipedia article about the lifeform Kinoko is capable of growing.
- Spore - Wikipedia article about the reproductive cell Kinoko can produce.
- Fungicide - Wikipedia article about substances that are highly effective against Kinoko's Quirk.