スーパーマリオギャラクシー
In "Super Mario Galaxy" and "Super Mario Galaxy 2", Mario and Luigi are able to transform into Boos themselves, through the use of the "Boo Mushroom" (a version of the series' famous Super Mushroom). In this form, the player is able to levitate and pass through certain walls, and being able to understand the Boos' language, "Booish".