From the Super Mario Wiki
Octopuses are enemies appearing in the games Super Mario Galaxy and Super Mario Galaxy 2. They are quite different from real-world octopuses, as they do not swim. Rather, they are giant, gray Octoombas with pale spots and a blue antenna. They are larger in size than their Octoomba sub-species and have two round body segments that look vaguely coil-like with four small tentacle feet at their bottom.
Super Mario Galaxy
The Octopuses from Super Mario Galaxy
In Super Mario Galaxy, these enemies mostly appear in areas with airships in them and they usually hide in barrels or stand on platforms until Mario appears within their range, after which they will try to shoot Mario with coconuts/watermelons or fireballs as their main form of attack. They are always found in pairs. To defeat them, Mario has to send back the coconuts they shoot by spinning. One pair that shoot only fireballs in the Space Junk Galaxy must be destroyed by the player throwing shells towards them. Octoposes usually guard bridges that will be released upon their defeat.
Super Mario Galaxy 2
Octopuses from Super Mario Galaxy 2
In Super Mario Galaxy 2, they reappear in the Shiverburn Galaxy where they act as the final enemy defense line before facing Prince Pikante. Similarly to the first game, they guard a pathway (of rock over lava) that Mario requires to progress. However, unlike its prequel, there are five instead of two. They also appear in the final galaxy, the Grandmaster Galaxy on the Platform Planet; this is their only appearance where defeating them is not mandatory to progress forwards. They still shoot coconuts and fireballs in this game.
Names in Other Languages
|From オクタロック (Okutarokku), the japanese name of Octorok