Ghost (Mini Mario & Friends: amiibo Challenge)
From the Super Mario Wiki, the Mario encyclopedia
Toy Boos simply called Ghosts appear in Mini Mario & Friends: amiibo Challenge as enemies. They levitate in mid-air, with some moving on a straight path (vertically or horizontally) from side to side, while others being stationary. Ghosts are invincible and, when in their active state, harmful to touch. However, they become harmless when they enter the light coming from a Candle. In this state, they are also forced to stop in place and cover their eyes, much like an actual Boo does when a character faces it in platform games, and the Minis are able to pass through them.