Keyzer

Keyzer, sometimes referred to as a Ghost Key , is a small levitating creature which bears some resemblance to a Boo, although with a key for a nose. They are seen in the Game Boy Advance game Wario Land 4, where one must be located by Wario in each of the eighteen stages. A Keyzer will always be found sleeping. Once found, it will wake up and follow Wario until he either loses all his health points, or exits the level via the Vortex. The Keyzer will then unlock the sealed door that leads to the next stage, and will disappear once it does so. Once the door is unlocked, the Keyzer cannot be found within that same stage a second time.

If Wario exits a stage without finding the Keyzer, his points and any Jewel Pieces collected will still be counted, he just won't be able to progress to the next stage. Wario is able to re-enter any stage where the Keyzer hasn't been found.

In the Crescent Moon Village stage, a ghost enemy called Yūrei shows an interest in Keyzer, and excitedly tries to steal him from Wario. Yūrei's movement will become faster after stealing the Keyzer, which may make it difficult for Wario catch him. Wario simply has to touch Yūrei to retrieve the Keyzer, although Yūrei will continue trying to steal it.

Keyzer also appears in volume 28 of the Japanese manga series "Super Mario-Kun", on the page showing the chapter's end.