Rolltergeist

Rolltergeists are enemies that inhabit Blowhole Castle in Wario: Master of Disguise. Twenty of them appear in a cluster in a secret room behind a white door that disappears if it is not entered quickly. Rolltergeists appear as a roll of bread with eyes. They attack Wario by rolling into him. Any attack will defeat them instantly, and they always drop two large gems upon doing so.

While the white door room the Rolltergeists are in is designed to be accessed with the spirit switches on, precise placement of Arty Wario's blocks allows it to be accessed with them off. Doing so reveals that Rolltergeists are not affected by the spirit switches, unlike most enemies in Blowhole Castle. It is unclear whether this was intentional or the developers simply did not think the player would be able to access the room with the spirit switches off.

In-game description
"The world's most talented baker put his heart and soul into creating the world's most perfect roll, only to have it spring to life and flee his kitchen."