I forgot to mention one amusing encounter with a cloaker in a recent play report. I could simply edit the post and add a paragraph but I’ve figured that I could do one of my « A note on … » article as I think it’s quirky enough.
So basically a cloaker in D&D is a manta-like intelligent predator that, as the name implies, ressemble a black cloak or a coat when it’s immobile.

The funny gimmick (for a DM anyway) is the mode of attack of this ambush monster: once a cloaker has chosen a victim it will silently glide from behind or jump unto an unsuspecting passerby that thought it just a piece of clothe or use its mind-affecting « moan » power but either way it will engulf its prey to bite it or perhaps just let it suffocate to death. Outside help is complicated by the fact that hitting the Cloaker much likely hits the engulfed victim too!
Aside: The always useful The Monsters Know What They’re Doing’s article (here) on the cloaker tactics mentions how the « suffocate » mechanic should be applied efficiently in 5E.
The first appearance of the Cloaker goes back to the 1981 Secret of the Slavers Stockade, a 40p dungeon-crawling adventure, the second part out of four of the slavers series. In it, the bad guys had some kind of understanding with this strange creature that came from far underground and it acted as a guard of sort for the slaves. Already at its origins it has all kind of funky powers to keep the players guessing!

Now, my version of a cloaker that I’ve put in my game does not have the appearance of a black cloak but instead looked like an authentic ancient tapestry, with some kind of complicated art on it, hanging on a wall inside the Tomb of Iyayo.

The emphasis I’m doing in this case is more on the MIMIC nature of the cloaker than being an exotic manta-like underground predator that happens to look like a cloak. Tapestries, rugs, and such will always be potential cloakers in my dungeons from now on. The neat thing I think is that my players, with the past few dungeons, are used to find clues on such accessories and so the dilemna will be: will you get close to this ancient looking tapestry that may give you an important clue knowing that it may well be a cloaker? ‘Cause that’s one of the best part of D&D, the « will you mess with this »? that you throw at the players constantly!