Chopper

Chopper also called E-28 Mecha Fish in Sonic Adventure, known in Japan as Bata-bata (バタバタ), is a badnik created by Dr. Robotnik in the game, Sonic the Hedgehog. This badnik is not very menacing, but some players can accidentally run into it when they are not aware of it (Which is very rare, because they are easy to notice). It is shaped like a fish, but mechanical. Near a bridge, it will keep jumping up trying to hit the player. In Sonic the Hedgehog 2 Chopper was replaced by an extremely similar badnik called Masher.

Sonic the Hedgehog (16-bit)
In Sonic the Hedgehog for the Sega Mega Drive, Chopper appears in the Green Hill Zone. It will simply keep jumping from under a bridge trying to hit the player. It is very easy to destroy, and nearly impossible to get hit by one.

Sonic the Hedgehog (8-bit)
In Sonic the Hedgehog for the Master System and Game Gear, Chopper has a different appearance. It will occasionally be under a bridge or by a waterfall with a bottomless pit. In Jungle Zone, there is only one of these that is actually menacing.

Adventures of Sonic the Hedgehog
Chopper made an appearance in the 1993 cartoon series Adventures of Sonic the Hedgehog. In the episode "The Last Resort", Scratch and Grounder release three Choppers to go after Sonic while he is water skiing. Sonic ends up tying his rope to the Choppers and water skis behind them.

Sonic the Comic
Chopper also made appearences in the British publication Sonic the Comic, as a member of Doctor Robotnik's badnik army.

Sonic Adventure/Sonic Adventure DX
In Sonic Adventure a robotic fish called E-28 Mecha Fish is said to be an upgraded Chopper and is one of the many fish that Big the Cat can catch.

Sonic Adventure 2/Sonic Adventure 2 Battle
Chopper appears in the unlockable Green Hill Zone stage. Instead of jumping up and down like in the original game, he jumps over the bridges in an arching motion.

Sonic & Sega All-Stars Racing
Chopper makes an appearance in two of the three seaside hill race courses as an obstacle.

Sonic the Hedgehog 4
Chopper returned as an enemy in Sonic the Hedgehog 4.

Sonic Colors
In the galactic Adventure game, Sonic Colors for the Nintendo DS and Wii, Sonic fights his way through an aquatic based zone called Aquarium Park. Throughout the six acts of this zone, schools of Choppers along with very large Choppers infest the many waters that Sonic encounters.

Sonic Generations
Chopper has been confirmed to appear in Sonic Generations as an enemy. In Green Hill Zone, a giant Chopper has been seen eating the grinding rails in an attempt to catch and destroy Modern Sonic. The giant Chopper reappears in Seaside Hill if the player attempts to abuse the hydroplaning effects of the Sonic Boost to leave the level's boundaries, causing Sonic to lose a life.

Trivia

 * Chopper's Japanese name, Bata-bata, is the Japanese word for a clattering noise.
 * In Sonic Labyrinth, a fishbot named Kapupu is similar to Chopper and Masher.
 * In Sonic the Hedgehog 2 (8-bit) a nameless enemy in the Crystal Egg Zone has a resemblance to Chopper.