Roger the Potted Ghost

Roger the Potted Ghost is a boss character from Super Mario World 2: Yoshi's Island and is located in The Potted Ghost's Castle, the castle of World 2. Roger starts out as a lifeless flower pot, but is transformed by Kamek's magic into a large ghost when the player enters the boss room. He is the only inanimate object that Kamek transforms into a boss. He's amorphous, but his face resembles Dangling Ghosts and Caged Ghosts.

To defeat him, the Blue Yoshi has to push Roger and his pot over the right edge of the platform in the same manner as pushing a regular vase. This process is complicated by two green Shy Guys that slowly push Roger in the opposite direction. Throughout the battle, Roger can lunge at the Blue Yoshi, knocking him away. He also breathes blue flames which home in, forcing the blue dinosaur to stop pushing and get out of the way to avoid taking a hit. When Roger is pushed far enough, the Shy Guys topple over the edge and do not return, allowing the Blue Yoshi to push him the final distance without facing resistance from them.

In Yoshi's Island DS, there are enemies called Potted Ghosts. They look much like Roger, only much smaller and less malevolent.

Trivia

 * The blue flames he shoots are based on the hitodama, a phantasmagoric phenomenon in the Japanese folklore which is said to be the souls of the dead.
 * Some stones are seen when he is pushed off the platform, implying that he falls through the floor.