Octoarcade is a first overworld boss in storymode, you have to shoot(hero shot) the screen with the hero shot while riding on the rails and ground, if the screen turns green, he will shoot shots from sides, if it turns red, he it will launch a bomb rush(Suction cups) , if it's cyan after you shoot the screen the tentacle will appear after you shoot it untop of it. Those goes on until phase 1. In phase 2, the arcade will build up more and sides meaning it's much higher and can move tiles on it, same things happen I'm phase 1 but it will aim much faster. Finally, in phase 3, the builds up again but higher at his limit which takes longer to swim up. He will fire tentamissles instead of firing shots, ride the rails to hit the screen until it's covered in ink, after the screen turns blue, you swim up on the sides to shoot the tentacle for the last time and then, he is defeated and grab the first zap fish.