I know it's early but speculation on Troll Biology and culture was always one of my favorite Homestuck aspects and so that's naturally translating over to the Nymphs now Satyrs. I've also been binging a lot of the Alien franchise so I'm just kind of in an alien mood lol.
Nymphs:
So I will begin with I don't believe that the Nymphs are what we think they are. I believe the nymphs are specifically the squid/octopus like creature that sits on the head, so Ly'lac would be the purple squid not the body we see, let me explain.
Ly'lac possess a xenomorph style second mouth, if you know anything about the Xenomorphs of the alien franchise is they are a parasitic species either through implantation into a host body or in some narratives eggmorphing using various secretions to slowly melt down and reshap a host into an egg the idea is they are a species that can't reproduce on its own they require another species.
Ly'lac also demonstrated the ability to grow extra limbs which you might find interesting there is a parasite that actually has that ability. It infects a host like a frog and can affect its development allowing it to grow extra limbs. Obviously for the sake of fiction and probably just making it easier to draw she can also undo her extra limbs but I find it interesting nonetheless.
Then look at the adult Nymph the caretaker she appears to basically be a full octopus creature, we know the nymphs go through some kind of metamorphosis but that seems like such a drastic change, no humanoid looking eyes or skin or claws or anything. This however make sense if the actual Nymph is just the octopus and their growing process is actually slowly consuming the host organism to mature into a full octopus. We already know nymphs are expected under certain circumstances to consume their own so this wouldn't be far remove.
So here is my proposal, a Nymph is a squid-like creature that latches onto the head of the host, its mouth burrowing through the skull to give us that second inner mouth we saw with Ly'lac. Over time it slowly consumes the host organism until it grows into a fully realized octopus/squid-like person like the caretaker. But of course you may then be asking who are the hosts?
Satyrs:
We are still early but through the power of in-universe anime images we have seen anime of people with horse ears and people of horse ears and with unicorn horns. We can probably safely assume that is more or less what Satyrs are going to look like much in the way troll movie posters were edited to be humans with horns.
Now Squiddles in Homestuck have some interesting unicorn-like things tide to them, such as the narwals they ride or this little bit a song called "The Day the Unicorns Couldn't Play"
(But... but where are the unicorns today, Mommy? Where are the unicorns?)
(Someday, when I'm older, I'll— I'll find Santa Claus. He'll bring the unicorns back, won't he Mommy? Mommy? Where are you, Mommy? Are you with the unicorns?)
I will propose to you that the host organisms that Squiddles sorry Nymphs use are Satyrs, latching onto them, riding their bodies, sucking nutrients to grow and mature. This then can explain there being two different types of Satyrs, beyond just Dirk loving horses and having watched MLP, the single horned satyrs could have arisen as an evolutionary defense system from Nymphs. A giant horn sticking out of your head is a pretty good way to protect from a brain squid from latching onto you.
It would be a very Rose move her to try to game the competition between their species by making it so her species specifically feed, conquer, and devour Dirk's in their life cycle while Dirk's species was then able to manifest horns as a defense mechanism against this so his species didn't immediately lose.
However there is that mention that the unicorns disappeared, this I believe is because in the history we have yet learned of.
Where Nymphs and Satyrs Play:
These species were designed to compete against one another, and if I'm correct they are designed to have one feed on the other. I think it be only natural if they eventually came to war and what would the Nymphs specifically want to wipe out? The Unicorn Satyrs, the Satyrs who had evolved to be unable to be used as Hosts, and so that's why the Unicorns disappeared and didn't get to play they were wiped out and the hornless satyrs were left and used as almost a slave-like class to be hosts to the Nymphs.
However I will go a step further and suggest that Vriska is at fault for this. Something odd happens when Vriska crashes into Deltritus, one second it's a normal looking earth-like world green and blue but the next second after she crashes into it, it glows pink and when we zoom in we now see the world is blue and pink. I believe Vriska either intentionally or accidentally caused some kind of knock-back effect on history and altered the world to be one where Nymphs won dominance almost like a retcon if you will.
In essence there are actually two Deltritus, one where the Satyrs were victorious and thus are the ones who are going to play the game and another where Nymphs are, basically it's almost like the world went through a scratch before the game even began. Of course split eras, timelines, universes, and even realities has never stopped communication before through the power of chat clients the Satyrs and Nymphs can communicate from their respective Deltritus, D.N.Alkyrin (alicorn and kyrin cute) being anime from the Deltritus where the unicorns never disappeared.
Which mean Rose and Dirk's game is already messed up, they both won, they both lost, and now both species will play.
The legendary Uninymph:
A figure we know little about and only learned today, but if I'm even partially right the uninymph truly would be a marvel. Either a nymph that managed to survive being speared by the natural defense of the Satyr horn....or a member that found a way for the two species to co-exist as one unit in a way that wasn't harmful. Which for a species designed to compete against one another I can already see why the Uninymph may have been one of a kind.
Fun fact there is potentially an interesting bit of foreshadowing to this earlier.
JADE: im growing orchids onto the trunk of this tree!
ROXY: they just grow hanging off the branch like that?
JADE: yeah! orchids are a type of plant called epiphytes, meaning they can survive off the backs of other plants instead of in the dirt
JADE: the roots attach themselves to the tree and after some aggressive loving and watering eventually they can grow on the tree all by themselves!
ROXY: ohh so theyre like mistletoe
JADE: well actually mistletoe is parasitic, they suck the water and nutrients straight out of the trees they grow on
JADE: orchids don't do that at all! they just use the tree like an anchor to get to their sweet spot so they can grow. for an orchid to kill a tree it'd have to be huuuuuge
So I would say that Uninymph could metaphorically be misletoe that somehow learned or biologic changed to be an orchid, perhaps they were a mutant among their species like the Signless/Karkat? It was born/or gained with the ability to latch onto satyr and instead of parasitically sucking away it instead merely anchored itself to a satyr and began to grow without needing to consume from its host.
I could be totally wrong about all of this, I just needed to get these ideas out of my head so my brain could calm down.
