From the Super Mario Wiki
Octoombas (also referred to as Electrogoombas and Octogoombas) are enemies that appear in many 3D Mario titles. They are very common aliens in most galaxies, and bear resemblances to Goombas and Octopus, both of which contribute to the name. They will give a warning by turning red, and moving their head back.
Super Mario Galaxy
Octoombas first appear in Super Mario Galaxy, in the first mission of the game. They reappear as common enemies in many galaxies after that. If Mario comes near one, it will headbutt him with its antennae. 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 are also two sub-species of them called Octoguys and Octopi.
Super Mario Galaxy 2
Octoombas re-appear in the sequel to Super Mario Galaxy, Super Mario Galaxy 2. Unlike in the first game, they won't headbutt Mario, but rather, they will spit rocks at Mario just like Octoroks. Their name is revealed to be Octoombas by a Luma who guides Mario through a large planet. Two new sub-species are also introduced: Elite Octoombas and Octoboos.
Super Mario 3D World
Octoombas re-appear in Super Mario 3D World as enemies in bonus world stages, first appearing in World Star-2, Super Galaxy, as common enemies. 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; thus they act similarly to Elite Octoombas. Octoombas are also much stronger than in the Galaxy games, as they are resilient to almost every attack (including Rosalina's Spin attack). They can, however, be defeated with a Ground Pound. They appear only in Super Galaxy, Gigantic Seasick Wreck, and Champion's Road.
Octoombas are alien-like Goombas. Their body style is exactly like that of a Goomba except for the antenna on top of their head. They have smooth, blue skin with yellow spots, a puckered round mouth and glowing yellow eyes. They attack with a headbutt or by spitting rocks, and only patrol a very small set area.
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.
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