Yochlol
Yochlol, the Handmaidens of Lolth, are demons which can manifest as an amorphous, somewhat drippy, yellow tree-like column about seven feet tall, with many branch-like arms each about ten feet long each and a single eye near the top. They are known to speak elvish.
The adventurers encountered a Yochlol and nearly slayed it before it rescued to another plane.