Octacon appears to be a small, cute pink octopus at first, whom Dedede believes to only like sardine. However, that's just a disguise; in his true form, he is an immense, crimson octopus monster with glaring green eyes.
He is a humongous, evil red octopus whose favorite food happens to be sheep and sardine. The fact that he ate several of the Cappies' sheep is the reason why Kirby crash-landed in Cappy Town. Before Kirby's arrival, the Cappies were suspicious of Dedede's pet octopus and went to Kabu for advice. He foretold that a pink Star Warrior named Kirby would come to the Cappies' rescue and defeat the monster, which is where Kirby's arrival came in. Dedede tried to make the Cappies think that Kirby was the monster eating up all the sheep, but the Cappies were so suspicious of his pet that they didn't believe him.
As Kirby arrived at Dedede's castle and went to look for his Warp Star, Dedede consulted with Nightmare Enterprises about Octacon and the N.M.E. Salesman told him to just give him time to grow on him. Dedede went to check on Octacon afterwards and was hypnotized into attacking Kirby until he crashed into one of his throne room's pillars, dropping the Warp Star. Octacon grew to his true, giant size and began to destroy the castle, sending his miniature versions to chase and trap Kirby on one of the castle towers. Tiff showed Kirby the Warp Star and that's when Kirby began showing off his power, sucking up the miniature Octacons, kicking them away with his spin attack, and then sucking up Octacon's fireballs and becoming Fire Kirby for the first time. Fire Kirby then easily overpowered Octacon with his ability, and, riding the Warp Star, blew the monster away from the castle with one last breath of fire.
Not only is Octacon just the first Demon Beast to be defeated by Kirby, but he is also one of the most evil Demon Beasts to appear in the anime, seeing how he gains such a title from his murder and devouring of several sheep, as well as his hypnotizing and manipulation of Dedede into attacking Kirby before showing his true form.
Octacon is a size-shifter who can grow to his true, giant size at will when he feels like it. He is a master of hypnosis, and can manipulate anyone he hypnotizes as he pleases. He can generate miniature versions of himself that attack his opponent, and can also shoot fireballs from his tentacles. He can also breathe fire from his mouth.