Mind you the manipulation of time and space isn't something unique to the Yith, but it is something that only the Yith have thoroughly mastered.
Elder things for example have some ability to manipulate time and know how to store things in extra dimensional spaces.
Though while there are creatures who can go through time easily (Hounds of Tindalos) that is more an innate ability then something that had to be learned or developed.
Not really no. If someone does have powers to a degree, they're either A: a Deep One hybrid, which eventually converts you into an immortal fishman, B: A hybrid of something else, like that one guy in Dark Corners Of The Earth (a video game) who turned out to be part Yith, C: Nyarlathotep in disguise, or D: Randolph Carter, who was basically Lovecraft's version of a self-insert, who does fairly well on his various encounters with the eldritch but mostly survives by running away from anything remotely significant.
Or Whately and his many children.
The thing is that... being empowered by the Great Old Ones pretty much means your gone.
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Also I am wondering about something
Shub-Niggorath is known as the "Black Goat of the Forest with the Thousand Young"
Which some people have interpreted to mean that she has a thousand young...
But I always interpreted it to mean that she has basically a large number that could be anywhere from millions to endless droves.
What do you think?
Then again I am also someone who believes that Nyanthothep doesn't really have a "limited number of forms" the number is arbitrary.