Octoper OA

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

Trivia
It's name is a modification of the word octopus, and is similar to the word october (オクトーバー).