Octopus is an enemy Badnik encountered in Gene Gadget Zone, the sixth level of Sonic 3D: Flickies' Island. It is similar to Sonic 2's Octus.
This yellow/purple robotic octopus occupies a fixed position on the floor of Dr. Eggman's lab. It functions essentially as a destructible gun turret, shuffling itself around to follow Sonic's movement and bombard him with blue projectiles. Attack with a spin jump or spin roll, and smash it to recover its organic battery power source, a red Flicky, and make Flickies' Island a slightly less dangerous place.
The name of this Badnik is conjectural, as no official name has been given to it. The name comes from the level editor in a development build of Sonic 3D that is included as a bonus feature in Sonic 3D: Director's Cut. Jon Burton has confirmed that the name was used in the original game.