Octus, called Octar (オクター) in the Japanese manual, is a Badnik from the 16-bit version of Sonic the Hedgehog 2 found in Oil Ocean Zone. It resembles an octopus, which tends to stay on the ground and then jump up to fire a bullet horizontally towards you, but it can still be simply taken out with a spin attack. A different behavior for this Badnik was discovered in the Sonic the Hedgehog 2 "Simon Wai" prototype, where the Badnik flies away after shooting its projectile.
Octuses return exclusively in the Wii U version of Sonic Lost World with a redesign, adapted to the art style as other Badniks in the game. They appear in Tropical Coast Zone 4, sneaking on water surfaces; in Frozen Factory Zone 4, floating up on the oil puddles and firing projectiles during the factory parts; and in Silent Forest Zone 3, skidding with their tentacles on the ground and shooting projectiles against the player.
They return in Sonic Mania, again in Oil Ocean Zone, with the same attack pattern. In addition, Mega Octus, the zone's boss, is a giant and more powerful version of this Badnik.