Bat Brains are robotic bats created by Dr. Eggman. These Badniks tend to hang from ceilings and drop down on unsuspecting enemies, diving at them head on. They made their first appearance in the original Sonic the Hedgehog game and have appeared in numerous games and other media since.
Sonic the Hedgehog (1991)
In their debut appearance, Bat Brains were encountered by Sonic in the Marble Zone. They would hang from ceilings in the stage's underground areas, dropping down when Sonic approached and flapping towards him. Sometimes a Bat Brain would rise up and return to hanging from the ceiling, others it would keep flying in one direction.
The classic Bat Brain would reappear in the mobile app game Sonic Jump. Appearing in the Blue Sky Zone, they would hang beneath clouds and drop down when Sonic approached. Unlike in Sonic 1, Sonic could not attack Bat Brain from any angle and could only hit its underside without taking damage.
Sonic Lost World
Bat Brains would return in Sonic Lost World with a slightly modified appearance; they had highlighted ears, their legs ended in circular hooks and they had mouths containing fangs.
Appearing in Windy Hill, Bat Brains behaved in a similar manner to their past appearances, dropping down from ceilings to attack. This time, however, they would always travel in flocks and attempt to swarm Sonic all at once. They were still easy to defeat as Sonic could simply wipe out a swarm of them with a chained homing attack.
In Sonic Mania, Bat Brains look and behave just as they did in the first game. This time, they are encountered in subterranean sections of the Green Hill Zone.
Sonic the Comic
Bat Brains were a mainstay of Dr. Robotnik's Badnik army before, during and after his reign over Mobius. Depending on the artist, their appearance would change on occasion. In the comics, Bat Brains were also sometimes armed with laser weapons built into their mouths or eyes.
Bat Brains were among the first generation of Badniks created by Dr. Robotnik when he conquered Mobius. During the early days of the First Robotnik War, Bat Brain would speak with a Transylvanian accent. Eventually, Bat Brains were rendered obsolete and decommissioned along with the rest of Robotnik's early Badniks.
During the Second Robotnik War, Dr. Eggman would recreate a number of his old Badnik designs, including Bat Brain. This new model would function more as a spy plane rather than a combat unit, though it was larger and appeared more intimidating.