Oblex

The Oblex is a new monster added to Dungeons & Dragons 5th Edition in the book Mordenkainen's Tome of Foes. The result of mind flayers experimenting on oozes, although Mordenkainen suspects Juiblex was involved somehow (probably because his name also ends in -blex), the Oblex devours humanoids to steal their memories and then can create exact duplicates of them except for a cord of ooze connecting them to the oblex. It is not possible for an oblex to replace an entire town's population with duplicates, however, because the most powerful version, an Elder Oblex, can have at max 13 people impersonated.

The Oblex was conceived with the help of a young fan, Nolan Whale, whose wish to work with the creators of D&D for a day was granted by the Make a Wish Foundation.

There are three categories, Spawn, Adult, and Elder. Spawns cannot impersonate, and are spawned from Elders when Elders absorb personalities but do not have any more space for new personalities.

Despite certain loose similarities, the Oblex shouldn't be confused with Obliviax, aka "Memory Moss" or "Oblivion Moss"; a thought-stealing moss that psionically drains the memories and minds from passers by and then uses that stolen psionic energy to shape crude duplicants made from extensions of itself. Or Obelix for that matter, though the name could be derived from "Oobleck".

The Oblex can also be seen as a more powerful version of the Impersonator, an ooze from Ravenloft that also disguises itself as people it has absorbed, but doesn't have access to their memories and can only impersonate one person at a time.

Interestingly, the artwork for the oblex spawn is from a different ooze creature, the graveyard sludge, found in the Monster Manual V. While not the first time that old artwork has been "repurposed", it is a bit depressing, given how the oblex came to be.

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  The graveyard sludge oblex spawn