Goku meets Octopapa when he went the opposite way as Bulma and Krillin due to General Blue's trap. Octopapa gets mad at Goku when he mistook him for a spider and made him want to eat Goku. Goku ends up frying him with a Kamehameha, and eating him instead. According to Goku, he tasted like chicken.
Video game appearances
Octopapa is fought in Dragon Ball Z: Super Gokuden: Totsugeki-Hen. He appears during the boss battle against General Blue in Dragon Ball: Revenge of King Piccolo and Blue hypnotizes him to attack Goku; Octopapa attacks with his tentacles and by blowing bubbles at the opponent. He is a boss by himself in Dragon Ball: Origins 2 where he attacks with one of his tentacles and causes rockfalls. In the bonus level 3-6, Bulma goes in the underwater cave alone to find the octopus, because it contains a nutrient that make the skin beautiful.
Octopapa (named Giant Octopus) was somehow reincarnated in Dragon Ball Z: Attack of the Saiyans, guarding the Five-Star Dragon Ball in the Pirate Cave. Goku comments that he is a squid to which Octapapa replies: "Why do I feel like I've had this conversation before?", referencing his first encounter with Goku. He also reveals that he was told to guard the Dragon Ball by the Red Ribbon Army.
Octopapa seemingly does not need to use his mouth to talk as shown in "The Pirate Treasure" when Goku attempts to clog his mouth with a rock, but Octopapa explains the boulder is not in his mouth but his nose. While explaining this, his mouth is shown and it is not moving.