I created an undead "Gothic Nothic" for my homebrew. One ability is its gaze causes a turn to stone effect, even when beheaded, (like a Medusa). It's on a Barbarian's shield right now. It's good for a laugh during combat.

Quote from RaifTwelveKill >>

Vax... You killed an NPC

AMAZING Mission complete! THAT right there is why you're the best Boss. The one and only!"

Being a D.M. playing as a Nothic is really fun, as long as the players don't chicken out because they have never faced anything more powerful than a Bugbear.

The Nothic was a surprise hit in my LMOP campaign. I used my characters flaws as ways to mock each of them. I had all of them nervous whispering all their insecurities to them.

Quote from TheDungeonDude >>

the first time I encountered tis thing I shit my pants

 Weekling. my party befriended it and turned it. Against the people in the people the lived in the place (we were trying to defeat them) and my brothers were obseced with it for the rest of the game but little do they know in my current campaign they are about to enter an area with bloodthirsty nothics

They could learn something like where the party is staying - then it could try and escape to turn into a bigger encounter later.

So ah I Have a magic city. I think I might use one or a group of these as librians in the deepest darkest parts of the library. Esiantally they run the restricted section of an academic library in a town wear almost anything goes. They keep the knowledge the most powerful mages in the world are afraid of.

These are also helpful in back stories of younger Wizards as a cautionary tale or boogeyman like tales for arcane practitioners who are far to eager to learn to much. Either told from parents, grandparents or just older mentors. 

My party managed to befriend the one in the redbrand hideout and they’re using it as a guard while they turn the hideout into an adventurers inn/guild thing. They also have a illusionist hobo they found in a dungeon that is going to be the innkeeper

Okay, so im just going to go ahead and start the controversy. Since Weird insight says uncharmable creatures are immune to its effects, that means Elves and Half Elves have Advantage on their Deception check to avoid it. As Fey Ancestry lets them have advantage on saves that cause the Charmed condition.

In addition, i would reccommend using the 2nd lvl spell Nondetection, which means you cannot be targeted by divination spells or seen through magical sensors, (while i still wouldnt rule that this makes you invisible to Nothics entirely, a creature under this spell should be immune to Weird Insight) it can be a bit pricey to continually cast though. 50gold worth of components each time.

Finally, the rare magic item Amulet of Proof against Detection and Location: it is attunement, but for a BBEG or a player who'se backstory is they are being hunted, this item is a godsend. It is a constant nondetection spell without the monetary cost and only requires an attunement slot.

Read a good bit of lore on these things. Apparently they were arcane casters who got a little too close to a secret that Vecna wanted to keep hush hush. 

I would also rule some of them being cursed, or willing servitors of Savras the unseeing. (Lesser diety of divination in Forgotten Realms)

Ah, but that is exactly it. Do you really expect the evil wizard turned Lich, turned God would WANT people to be able to do what he did?

If i were a maniacal overlord bent on bending the universe to my whims the last thing i would want is some upstart using the techniques that i spent millenia inventing from the ground up to pull the rug out from under me and take the universe himself.

The reasonable solution? Curse the everloving crud out of them and eliminate their memories, including the memory of the key secret they discovered.

why does it have only one eye

Quote from Ebotts >>

Can we please get an in-depth expansion of this super-weird creature, along the lines of the excellent entries in Volo's Guide to Monsters? Questions worth addressing: Since they can't understand the memories of their past lives, I would assume many of them can't remember their names from life. So, what sorts of names do they use? If they don't use names for themselves, what names do other intelligent creatures call them by? The fact that they have an ability dedicated to learning the secrets of other creatures, which suggests that they crave not only arcane knowledge, but intimate personal knowledge as well. And yet they are "content to watch" most of the time, which implies that they are quite solitary. There's an interesting tension here between desiring information gleaned (normally) from social interaction but also shunning such interaction. What is behind this tension? Why did Vecna leave this curse, if he himself is (or was) a lich, which means he too devoted his life to unearthing arcane secrets?

It feels like there's so much under the surface! I crave more! Give me all of your secrets!!!

He's the god of secrets, not the god of information known only to some.  It's like how a god of trees and a lumberjack both base their existence around trees, but the god isn't going to like the lumberjack that much.

Also craving to know the secrets of the nothics might just result in you learning those secrets the hard way.

Probably deep back story secrets

my party ate it

I just tamed one with the corpse of a random goblin and decided to call it norman

Holy shit this is cool. My players new favorite monster.

My character died to this

I wonder if I should stay as a nothic because right now I am cursed and am a nothic.