Monster Monday - Balhannoth https://www.dndbeyond.com/monsters/balhannoth
Balhannoths are terrifying aberrations that dwell primarily in the Underdark and the Shadowfell. They look like eyeless beholders with long tentacles, each of which has a paddle-like appendage that has sharp tooth-like spines on it. The Balhannoth cannot fly, but it can teleport and go invisible and it attaches to ceilings and overhanging branches and other types of things where it waits for prey. It can use legendary actions to teleport away with a creature it has just attacked and grappled, and it can use powerful psychic attacks to make passing sentient beings believe they are close to places of safety or close to something that is their heart’s desire.
Have you ever fought a balhannoth? Have you ever used one against a party of adventurers in a campaign you were running?