Octoper OA

Octoper OA (オクトーパーＯＡ), known as Octoboss in Mega Man for Game Gear, is a giant octopus robot that appears as the sub-boss in Wave Man's stage, appearing while Mega Man is using the marine bike. It bobs up and down in the water, and can only be damaged in the green core on its forehead. When its face appears, it will shoot energy balls from its mouth. The Octoper OA in the Mega Man Game Gear game is smaller than the one in Mega Man 5 on the NES.

Trivia

 * Octoper OA's name is a modification of the word octopus, and is similar to the word October (オクトーバー). Because of this, its name is mistranslated as "October" in the Navi Mode of Mega Man: Anniversary Collection.
 * Octoper OA would also have been able to attack with a tentacle, but this was removed from the game.
 * Octoper OA is the only sub-boss in Mega Man 5.