Fishbone

From the Super Mario Wiki

A Fishbone.

Fishbones are swimming skeletons of fish found in the game Super Mario World. They always swim in a straight line, heading to the left. Fishbones cannot be defeated. Even the powerful Yoshi can't destroy them. However, Fishbones swim very slowly, so avoiding them is not too hard. Also, Cape Mario or Cape Luigi can destroy them by spinning.

Official artwork of a Fishbone.

Fishbones may be the undead sub-species of Cheep-Cheeps and/or Blurps. These skeleton fish may even be related to the Honens (the undead form of the Torion), an enemy only seen in Super Mario Land. Another relative could be Jean de Fillet, an undead fish from Super Mario World 2: Yoshi's Island.

Fishbone is also the name of the useless item that Mario sometimes receives after being thrown in the trash can in the Mario Bros. Battle mode of the Super Mario Advance series. Although here, they were called "Fish skeletons".

Kingfin from Super Mario Galaxy is perhaps related to these creatures, and maybe even be their king.

[edit] Appearances in Other Media

Fishbones, though never called as such, made several small appearances in the Super Mario World cartoon.

A Fishbone first appeared in the episode "The Wheel Thing", where one is used by Yoshi to cut a log into wheels to be used in Mario's car factory. In "The Night Before Cave Christmas", both Mario and Oogtar use a Fishbone to cut-down several Christmas trees.

In "Rock TV" and "Mama Luigi", two extremely large Fishbones are shown to be decorations in Bowser's throne room.

In the Super Mario Adventures comic, Fishbones, along with several other creatures such as Urchins and Porcu-Puffers, are shown to act as guards/obstacles in the moat surrounding the Koopalings' tower.