Octoomba

An Octoomba, once called Electrogoomba in Prima's Official Guide and the Super Mario Galaxy Trading Cards, is an enemy that first appeared in Super Mario Galaxy. It is an alien very common in most galaxies, and bears a slight resemblance to Goombas and octopi, both of which contribute to its name.

Super Mario Galaxy
Octoombas first appeared in Super Mario Galaxy. They are seen in many galaxies of the game. If Mario comes near, they will headbutt him with their antennae. Once they are defeated, they each leave behind three Star Bits or a coin if they are spun or jumped on, respectively. There are also sub-species of them called Octoguys and Octopuses.

Super Mario Galaxy 2
Octoombas re-appear in the sequel, Super Mario Galaxy 2. Unlike in the prequel, they won't headbutt Mario, but rather, they will spit rocks at Mario. Their name is finally revealed to be Octoombas. New sub-species were also introduced such as Elite Octoombas and Octoboos.

Appearance
Octoombas are odd-looking creatures. They have smooth, blue skin with yellow spots, a puckered round mouth, glowing yellow eyes, and a small antenna on top of their head with a glowing yellow organ at the tip. They attack by recharging and then headbutting Mario with their antennae, and only patrol a very small set area. They could be killed by simply jumping on them or by spinning them. When jumped on, they get flatenned like a pancake and disappear, like a normal Goomba. Although they are weak, their headbutts are seen to be strong, as they can knock down Mario and stun him for some seconds. In Super Mario Galaxy 2, they attack by recharging and spitting rocks, and they don´t knock down Mario in this game. They also turn orange when they recharge.

Sub-species
A pink sub-species is known as an Octoguy, and is somewhat smarter than the standard one. It attempts to run away from Mario if he gets too close and will spit rocks at him once at range.

Another sub-species of Octoomba is gray, and taller and bigger then the other two, called an Octopus. It is immobile, but can shoot projectiles at Mario. Some Octopuses shoot either coconuts or fireballs, and others only shoot fireballs, similar to Birdo in her Super Mario Bros. 2 appearance.

Super Mario Galaxy 2 introduces the Elite Octoomba, a green Octoomba with the ability to shoot two boulders, one after the other.

Trivia

 * Octoombas resemble both Octoroks and Deku Scrubs from many The Legend of Zelda games.
 * Octoombas have a similar appearance to the Bloopers found in Super Mario Sunshine.
 * Their voice sounds similar to that of the Shroobs.