Oblexes were extraordinarily intelligent oozes created by mind flayers that fed on other creatures' memories. They were capable of using those memories to create replicas of their victims, which they used to further hunt and feed.
As oblexes absorbed the memories of their victims, they could replicate credible copies of them. These impersonations, made of the same ooze as the oblex, were otherwise identical to the original victims, except for a faint smell of sulfur. They could move up to 120 feet (37 meters) from the oblex, but could not entirely separate from its body. A replica remained attached to the oblex's main body by a thin, transparent tether made of slime, which could pass through extremely tight spaces as narrow as 1 inch (2.5 centimeters) wide.
Oblexes were attracted to sharp minds. They tended to prefer the minds of intelligent individuals, such as spellcasters. When finding a suitable individual, they proceeded to briefly engulf their target's body, draining a portion of its memories when pulling away. An affected victim became drained and confused, having difficulty recalling or using any abilities. At the same time, the oblex learned all of its victim's languages and abilities.
Cunning hunters, oblexes used their impersonation abilities to lure more victims into danger or to attract better sources of nourishment.
Oblexes preferred luring their victims to an ambush before attacking, by using their impersonation abilities. Besides their memory-draining attack that could render a victim unconscious if hit multiple times, they were also capable of physically slamming an opponent using their pseudopods.
As oblexes aged, they acquired more powerful abilities. Adult oblexes had the ability to cast mind-controlling spells such as charm person, detect thoughts, hold person, and color spray, while elder oblexes, having lived long enough to learn multiple abilities, could in addition cast spells such as confusion, dimension door, dominate person, fear, hallucinatory terrain, hold monster, hypnotic pattern, and telekinesis.
The oblex reproduction cycle was intrinsically connected to its feeding habits. As an oblex fed, it slowly became saturated with its victims' accumulated memories and personalities. Eventually, a saturated oblex had to split into smaller creatures in order to avoid going insane.
Oblexes were designed by mind flayers with the purpose to serve as advance scouts to search for prey to feed a colony. However, oblexes did not act on their master's orders. Rather, their actions were purely motivated by hunger. An oblex within the telepathic range of an elder brain would instinctively, and unwittingly, inform the colony of any sentient creatures just by its endless hunger for memories and attraction to intelligent individuals.
In the late 15th century DR, an elder oblex stood guard in a chamber of the Temple of Madness in Pandemonium, while a group of mind flayers attempted to harness the power of a portal to the Far Realm to activate an artifact that could allow them to regain their mental control over the gith. A group of Sha'sal Khou members from the Sword Coast was dispatched to thwart the illithids' plans.
- Mike Mearls, Jeremy Crawford (May 29, 2018). Mordenkainen's Tome of Foes. Edited by Kim Mohan, Michele Carter. (Wizards of the Coast), pp. 217–219. ISBN 978-0786966240.
- Chris Lindsay (2018-05-29). Rrakkma (DDIA-MORD) (PDF). Edited by Claire Hoffman, Travis Woodall. D&D Adventurers League: (Wizards of the Coast), pp. 3, 6, 8.
Brainstealer dragon • Gnome ceremorph • Gnome squidling • Mindwitness • Mozgriken • Tzakandi • Uchuulon • Urophion
Brain golem • Cranium rat • Nyraala golem • Illithidae • Illithocyte • Intellect devourer • Mind worm • Neothelid • Nerve swimmer • Oblex • Oortling • Ustilagor