The Octus is a type of Badnik created by Dr. Eggman that has appeared throughout the Sonic the Hedgehog franchise. It is an octopus-shaped robot that typically floats in the air and fires projectiles from its snout.
Sonic the Hedgehog 2
The Octus makes its debut in Sonic the Hedgehog 2's Oil Ocean Zone. Usually found in stair sections, they remain motionless until the player draws near, at which point they will jump up and fire a projectile at the player. They can be easily destroyed with either a Spin Jump or Spin Dash.
An unnamed Badnik resembling Octus appears in the Gene Gadget Zone in Sonic 3D Blast. Remaining still, these Badniks are usually found on ledges and will turn their heads to fire a series of projectiles at Sonic. Like all other Badniks in the game, this robot contains a Flicky inside that must be released so that Sonic can progress to a new area.
Sonic Lost World
In Sonic Lost World, Octuses appear in multiple stages and have a greater range of movement. In Tropical Coast Zone 4, lone Octuses can be found sneaking on water surfaces. In Frozen Factory Zone 4, some Octuses will float up from oil pools inside the factory section and fire projectiles. Finally, in Silent Forest Zone 3, Octuses will skate with their tentacles towards the player while firing projectiles.
In this game, Octuses retain their appearance and attack strategy from Sonic the Hedgehog 2. They are encountered in Oil Ocean Zone.
Adventures of Sonic the Hedgehog
In the Adventures of Sonic the Hedgehog television series, an Octus appeared briefly in the episode "Untouchable Sonic" where it and other Badniks chased after Sonic underwater only to be caught in some seaweed.
Sonic the Comic
Octuses only made a few brief appearances in STC. They were shown to be capable of flight and firing lasers from their snouts. Some even had extendable tentacles that they would use to capture targets.