The Octodiver is a variant of the Octotrooper and the Twintacle Octotrooper.
Unlike their regular counterparts, Octodivers are equipped with snorkel masks and hide in pockets of Octarian ink. When Agent 3 approaches them, they will quickly surface from the ink and begin firing. They are able to dive into their own ink when under attack or too far away from their target as a means of defense. Octodivers can have two tentacles, making them a Twintacle Octodiver, or just one, in which case they are normal Octodivers. In Splatoon 2, after diving into their own ink, ink patterns can be seen as where they last submerged.
Octodivers' most distinguishable feature is probably their mask resembling the Inklings' Snorkel Mask which can be purchased at Cooler Heads. Octodivers have light green eyes rimmed with purple, and their pupils are gray-blue. Octodivers, like Octotroopers have one to two red tentacles with multiple suction cups and a light cream underside to match that of their bodies. They rest upon blue-rimmed kettle-like machines.
An Octodiver sitting in a puddle of ink.