Octo, originally known as Scowler, is a big squid that first appeared as one of the bosses in Wario Land 3.
Wario Land 3
In Wario Land 3, Scowler is the boss found in Sea Turtle Rocks. His main attack is to try to grab Wario. If he does, Wario will be thrown out of the cave. At the first time, his weak spot is on his head, Wario has to touch it which will damage the creature. Then, the weak spot will move to his underside. He sometimes attacks with ink to turn the water black and prevent Wario from seeing, he only sees his head. After been hit enough times, he'll fail and leaves a ring behind him which helps Wario access the Grey Chest which contains the third of the five music boxes.
Dr. Mario 64
Scowler, now renamed Octo, reappears in Dr. Mario 64 as one of the enemies Dr. Mario or Wario have to face.
Unlike in his original appearance, Octo's body is coloured orange rather than black in the American release of the game. In the later port of the game released in Japan as part of Nintendo Puzzle Collection, he retains his original black colour scheme. His appearance may have been changed in Dr. Mario 64 due to a possible resemblance to blackface actors, similar to another situation faced by Nintendo with one if its Pokémon, Jynx.