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 and Super Mario Galaxy 2. 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 revealed to be Octoombas by a Luma guiding Mario through a large planet. 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 with a headbutt or by spitting rocks, and only patrol a very small set area.

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. They, especially in large numbers, are some of the hardest enemies to defeat in the entire game.

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.

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.''

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.
 * Octoombas also bear a resemblance to Shrooblets from Mario & Luigi: Partners in Time.
 * Octoomba's names are a combination of the word Octopus and the word Goomba.