Octoomba

Octoombas, originally referred to as Electrogoombas, are alien enemies that first appear in Super Mario Galaxy. They are very common, appearing in most galaxies, and bear resemblances to Goombas and Roctos, both of which contribute to the name.

Super Mario Galaxy
Electrogoombas debut in the first mission of Super Mario Galaxy and reappear as common enemies in many subsequent galaxies. If Mario comes near one, it will try to headbutt him with its antenna. They can be defeated by spinning them or by jumping on them. Once defeated, they leave behind three Star Bits (if they were spun) or a coin (if they were jumped on). There is also a timid, rock-spitting variant of them called Octoguy, and a large relative called Rocto.

Super Mario Galaxy 2
Octoombas reappear in Super Mario Galaxy 2 under their current name. They attack Mario by spitting rocks at him, just like Octoguys. Two new variants are also introduced in the game: Elite Octoombas and Octoboos.

Super Mario 3D World / Super Mario 3D World + Bowser's Fury
Octoombas return in Super Mario 3D World and Super Mario 3D World + Bowser's Fury as enemies in bonus world stages, such as Super Galaxy, Gigantic Seasick Wreck, and Champion's Road. Octoombas are the last enemies to be introduced in the game. Their attack pattern has changed once again - they now spit three cannonballs (although they can be jumped on) in a straight line instead of a single rock. Octoombas are also much stronger than in the previous games, as they are resilient to almost every attack (including Rosalina's Spin attack). They can only be defeated with a Ground Pound. Octoombas are now stationary, and only rotate in position, instead of moving back and forth.

Dr. Mario World
Octoombas appear in Dr. Mario World as assistants. They also appear in the background of World 8 when an area has been cleared. In stage mode, its effect is to fill the skill meter by half of the doctor's full gauge on stage start. In versus mode, its effect is to reduce the time before the stage starts shrinking the playing field by a percentage, which can stack with Scuttlebug's versus effect to further reduce the time.

Super Mario Galaxy

 * Trading Card description: "This class of Goomba, the long time Mario enemy, is adapted for space. These alien Goombas are found in many areas of the game and attack Mario by trying to headbutt him when he comes near. They can easily be destroyed by jumping on their heads. Electrogoombas are amphibious and have brown, red, and blue subspecies."

Dr. Mario World

 * Stage mode: "Grants 10%/20%/30%/40%/50% chance of half-full skill meter on stage start."
 * Versus mode: "Decreases time until your and your opponent's stages begin to shrink by 10%/20%/30%/40%/50%."

Description
Octoombas have a similar physique to Goombas. Their bodies are blue with several yellow spots, and they have small snout-like mouths which they use to spit rocks. Octoombas have antennae on their heads, and three rounded feet. They use these feet to hop from side to side to move. They have sunken glowing eyes and their brows are set in a scowl. When charging up their attacks, Octoombas will glow orange.

Trivia

 * Octoombas resemble both Octoroks and Deku Scrubs from many The Legend of Zelda games.
 * The data for Super Mario Galaxy contains a model for an unused enemy resembling a cross between Rocto and Electrogoomba under the filename "OtaJack."