Curse of Strahd
The Ghrom is an undead creature that seems somehow linked to the creation of the biomantic pods that are currently keeping the Martikov children in stasis, sapping their life essence. To what end this is, who controls it, and if there are more than one, remains mysteries. The PCs destroyed a Ghrom that was nesting in Mordenkainen’s mansion, alongside the Mordenkainen thing that was actually a host for an Illithid intellect devourer.
It has the ability to nest inside a humanoid, bursting from its host at will and retaining its skeleton. It uses a worm like tentacle to nest in the host’s gut and sprouts from the mouth as a tongue-like appendage which can sting and paralyze its victims, which then become the next host.