Octoomba

An Octoomba, once called Electro Goomba in Prima's guide for Super Mario Galaxy, is an enemy who made its first appearance 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
They are seen in various parts of the game and headbutt Mario when he approaches. In some cases, if Mario destroys some, a secret may be unveiled, as seen on several Airships in the game, where Mario had to eliminate two of them to make a bridge appear. They can easily be squashed. When jumped on, a Coin is always left by them. When a Star Spin is used to defeat them, they leave three star bits.

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 shoot boulders at Mario, similar to their pink sub-species (which still appear) and their name is finally revealed to be Octoombas. New subspecies were introduced; an undead variant of them with the ability to float and a green version that can shoot two boulders instead of one.

Appearance
Octoombas are odd-looking creatures. They have smooth, blue skin with yellow spots, a puckered round mouth (like a Snifit's), 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, and only patrol a very small set area.

Sub-species
One sub-species is a pink color, and is somewhat smarter than the standard one. It attempts to run away from Mario, and will spit rocks at him if he gets too close.

Another sub-species of Octoomba is gray, and taller and bigger then the other two. It is immobile, but can shoot projectiles at Mario. Some Gray Octoomba shoot either coconuts or fireballs, and others only shoot fireballs. As the forms become more powerful they look more like octopi. In fact, in Super Mario Galaxy, there is a Toad who refers to the Gray Octoombas as "octopi".

Super Mario Galaxy 2 features new yellow/green colored species, which apparently shoot multiple rocks in a row.

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.