Upon touching a Mystery Mushroom, Mario will be transformed into Costume Mario, Allowing him to take the form of one of many different costumes. Many of these costumes are based on characters outside of the Mario universe. Completing the 100 Mario Challenge Mode on a specific difficulty will unlock many of these costumes. Players can also scan any compatible amiibo, and some can be unlocked by completing an Event Course.
Mystery Mushrooms share the same effect as an regular Super Mushrooms, as they give Mario the strength to destroy Brick Blocks and give him an extra hit point. The only difference is that Mystery Mushrooms will maintain Small Mario's size, or (depending on Mario's current state) will shrink him down to that size.
- Mystery Mushrooms share a similar function to character caps from Super Mario 64 DS. They both allow Mario to transform into other characters. However, a Mario wearing a cap will retain his original voice and gain the other character's abilities. In most cases, the opposite happens with Costume Mario.
- While Mystery Mushroom are absent from Super Mario Maker for Nintendo 3DS, it is possible for players to make them appear through two glitches. When touched, Mario will become Small Mario, but is still able to break blocks and is given an extra hit point. It is also shown with a different sprite when the player holds down or .
- Not only that, Mystery Mushrooms are also absent in Super Mario Maker 2.