BFish is a scrapped Badnik found in prototype versions of Sonic the Hedgehog 2. The "BFish" name comes from source code found in the Nick Arcade prototype of the game.
Like other fish-like Badniks, BFish has the appearance of a mechanical piranha. Unlike Masher which simply leaps up and down with no horizontal movement, BFish attacks Sonic in an arc-like motion. To destroy the Badnik, the player should simply roll or jump into it.
BFish is a placeable object with edit mode in Hidden Palace Zone (or "Spring Yard Zone", as it's called there) in the Nick Arcade prototype (along with Gator and Stego). It can also be accessed in the Simon Wai prototype by hacking, though it was removed from the final game altogether.