Operation Octo is a tower defense action game where you play as Dr. Odin, an octopus scientist working with his dolphin colleague to destroy the skeletal invaders terrorizing the underwater ecosystems. The core gameplay involves strategically placing mechanized sea creature turrets like the Pistol Shrimp, Navy Seal, and Death Ray to fend off waves of skeletal enemies, but when defenses fail, the game turns into a frantic survival game that requires quick evasion skills.