These creatures take the appearance of a floating octopus with a large eye and several smaller ones, They are either regular types that can be defeated by red or green, they release Ruborian Fighters or they take the form of a blazed version that are immune to red's fire attack, and spawn Ruborian Bombers. These Overseer's are found later in game, and only during Kahn's Rampage. Each type either release fire or poison magic gas from beneath them.
Not much is known about these creatures although Jewel or Kahn uses them to summon raiders for attacking locations. Overseers likely come from magical locations or burnt locations such as ancient forests or volcanic mountains. In Overlord 2 overseers were likely killed from The Great Cataclysm or were captured migrating to other lands by The Glorious Empire. Kahn mentions The Wizard, which had been possessed, gave them to Jewel and himself.
Asides from sandworms these are one of the enemies you cannot defeat in the tower arena. They can only be killed if you are above their floating bodies, if you go beneath them into their dangerous magic or fire area, your minions will be immediately killed and you can lose nine bars of health within 2 seconds of contact. They are somewhat similar to Flamer Dwarves in attack, only killing in a Y axis and never ending.