Chedean Eye Tower (Huge Aberration) - CR 26

The Veteran and the gang are now inside a Xareth'Chelde (Beholder) hive, having struck a bargain with a Green Dracane (Dragon) and its Ssethrek (Lizardfolk) armies to work together to overthrow the Hive Mother, Blebb. However, getting into the structure required more than a little misdirection, powerful druidic spells, and an underwater battle with an Eye of the Deep and its mutated crocodile pets..

..They also came close to encountering one of these...

A construct molded from aberrant flesh and diseased solidified nightmares, these things tower some 40ft high, and are large enough to protect multiple Beholders, Squads of Lensmen and other Cheldean troops.

Art from:

The towers are hulking masses of boiling, warped flesh, studded with huge, alien eyes. Some are stalked, others are flush with the diseased surface. From the bottom of the tower extend thick tentacles of flesh and thorny chitin, and many have drooling, slit like mouths, lined with rows and rows of sharp, inward curved teeth and rippling with peristalsis on the lower parts of their bodies, though these are rarely coodinated enough to bite or cause harm...