The moon plot as a whole is horrifying, as it's such a massive departure from what Hermitcraft has always been in terms of subject matter and tone. It's like if your favorite children's TV show suddenly became a Cosmic Horror Story.
The fact that, when people first took notice, the moon had already been getting bigger for weeks. The change was so gradual, nobody could tell until it had become nearly twice its original size. And from there, it only continues to get bigger and bigger, until it doesn't even fit on people's screens anymore. Seeing the gigantic moon hanging in the sky at night is an incredibly uncomfortable and horrible feeling.
The effects of the approaching moon are similarly unsettling, starting off small but slowly ramping up in intensity, until they're a constant, terrifying reminder of what's happening.
The first effect was the earthquakes. They started off small and subtle, but slowly grew in intensity and frequency, until they were occurring at least ten times per hour, lasting around five seconds each. And they are violent, enough to force Hermits to stop moving and wait for the quake to pass to avoid accidentally hurting themselves. In the real world, they would likely be strong enough to level buildings.
The second effect was the floating. At first, Hermits would briefly float off the ground before dropping back down, something so small and infrequent that the first few instances were chalked up to server lag. However, Hermits then started floating more frequently, and much, MUCH higher, to the point that it actually started to disrupt things like building sessions. Eventually, gravity got so messed up by the moon's approach that every Hermit gained a permanent slow falling effect, while still intermittently being pulled up into the sky.
The third effect, also related to gravity, was the floating blocks; the moon's gravity pulling blocks out of the ground before letting them fall back down. The first few instances were hard to spot without pausing or rewinding videos, with the first few Hermits to spot them wondering if they were seeing things. However, the blocks got pulled up more and more often, higher and higher, until the earth itself almost looked like it was boiling... And then they stopped coming back down.
The fact that, despite many of the Hermits making efforts to stop the moon, there is absolutely nothing that any of them can do. Gem and False's Doomsday bunker will make them feel safe, but it won't survive the impact of an entire celestial body. The Mooners and the Order of Octa are both devoted to worshiping the moon, but intentional sleep deprivation and human sacrifices will not help pull the moon back into orbit. Cleo's plan to use TNT to move Hermitcraft itself out of the way, or Tango's plan to blow the moon back out to its original orbit will not work at all, because detonating explosives on the surface of a planet to shift its orbit without causing a life-as-we-know-it-ending apocalypse is like trying to move a truck by blowing on it. The only Hermit with a viable plan is Scar, and his entire scheme consists of "cram as many people and items as possible into a rocket and bail." As a result, the Hermits just go about their day, pretending everything is just fine, because the only alternative is to hide in a hole and wait for the end of the world.
The Mooners and the Order of Octa deserve special mention. The former believe that the Moon is the Great Lunar Neighbour coming to server to punish Hermits for constantly sleeping through the night and they burn their beds and forgo sleeping to hopefully drive the Moon away. However, sleep deprivation quickly starts to set in. Mumbo and Grian, who joined first, eventually started to suffer from visual and auditory hallucinations, like Phantom shrieks becoming the demented laughter or Mumbo seeing Grian with his skin sideways, both of which came absolutely out of nowhere. The latter are borderline Lovecraftian cult formed by Ren and Doc after they began to hear the voices from the moon rock that fell on their base. During the episode immediately after, Ren confesses to feeling mental distress and decides to write a diary, trating viewers to what was essentially a Sanity Slippage, as he tried to piece together why he remembered a massive amounts of potato-trivia that he has never learned, which after few days spirals into obsession about them... Then he starts Hearing Voices again and, obeying them, he and Doc launch a killing spree, slaying Mumbo, Grian, Impulse, Joe and a few other Hermits, before finally killing each other.
During Tango’s mission to save the world, he ends up having to stop at a Pass & Gas for rocket parts. The conversation he has with Keralis during this moment is downright unnerving, featuring him constantly contradicting himself, overlapping dialogue like he has no idea Tango is speaking, and phrases repeated with the exact same inflection. He doesn’t even recognise Tango until he takes his helmet off! The most terrifying thing, however, is that he mentions having been in space for months, and has no knowledge of the moon crashing, when Keralis’ most recent episode was only released two weeks before this interaction, and it featured Keralis trying to escape the moon, so who was Tango talking to?
And in the end, the moon does destroy the server. Some Hermits escape (the Boatem crew drops themselves through the Boatem hole, Gem creates an amethyst portal into another realm, Cleo flees to the End), but those that are left behind can only watch, helplessly, as the moon comes crashing down for real. We get treated to a (frankly stellar looking) animation of Boatem's portal being ripped apart, Gem's base being obliterated by space debris, and Grian's villagers panicking, all the while the server is cast in a bright orange glow as the atmosphere creates enough friction for the moon to start to burn. And then... kaboom.
While every Hermit has their own plan for dealing with the apocalypse, most of their fates are absolutely horrifying in their own right.
The Boatem crew drops themselves through the Boatem Hole, and wind up stuck in what appears to be the Void Between the Worlds. While they're still together and seem relatively okay with their situation, they can't do anything except wait to either die of dehydration or crash into something.
Xisuma, Cleo and Gem escape into the Nether, the End, and some kind of extradimensional amethyst portal respectively. While it's not clear where Gem ended up, Cleo's episode's Stinger shows her approaching the End's exit portal... only to find it inactive. And with the moon's gravity shown to have ripped Nether portals apart, it's not unreasonable to assume that Xisuma is now trapped in the Nether, just as Cleo is trapped in the End.
Tango attempted to save Hermitcraft at the last second by setting off explosives on the moon's surface to blast it back into its normal orbit. His supercomputer Holsten attempts to guide him through the process of finding highly volatile iridium crystals on the moon's surface, and leading the hostile moon bunnies away from them — but Tango's rocket is destroyed by space debris, causing him to lose contact with Holsten. Tango attempts to set up the explosives solo, but one of the bunnies steps on the pressure plate while he's still setting up the TNT, setting off the explosion too early and launching Tango into deep space, while the moon continues to fall.
Bdubs appears to have gone into hard denial, claiming everyone's bases for himself, relishing in the fact that Big Eyes no longer has competition, and talking about how great it is that the entire world is his now. He appears to not even be aware that the moon is falling... until you watch Tango's POV, in which Bdubs has sent him a message in a panic, saying that the entire world is falling apart, and begging him not to come back down to Hermitcraft. Bdubs's denial wasn't a symptom of stupidity, it was his way of coping with his impending death.
Ren's episode reveals what's actually been going on; Hermitcraft Season 8 has all been a simulation. The Hermits are all in cryo-stasis aboard a Sleeper Starship, on its way to the next season. The Hermatrix, the supercomputer in charge of keeping their minds active while in suspension, has been infected with a virus called the Nothing, with as goal to wipe the minds of the Hermits. As a last resort, it created the world of Season 8 to keep their imaginations alive, and sent instructions to Ren and Doc to create anti-virus measures, before sending the moon crashing down onto the server to eliminate the Nothing. However the question remains, who would make a virus to wipe the minds of so many people? And why?
The cutscene also has an... unnerving end. The Hermatrix alerts Renbob and the Goatfather — the pilots — to the fact that there's an intruder on board. Thinking the Hermatrix is just mistaking the life signs of the Hermits coming out of stasis for a foreign invader, Renbob has it do a full system scan. After putting the Hermits back in cryosleep, the scan results come back... fine. The Hermatrix is not malfunctioning... so who has snuck on board?
Season 9
The Rift under the Grian's base is... unnerving, to say the least.
Some time later Grian accidentally falls through the hole in the Rift's cave and survives, despite the height that should kill him. He then looks at The Rift, thoughroughly weirded out. Which either confirms The Rift's supernatural nature or suggests an existence of another force.
Then, The Rift unveils part of its true nature when Grian finds in the cave... Grumbot. The old AI is quite different than he remembers, which it explains as it comeing form Alternate Timeline of Season 7, where Mumbo did become a mayor of shopping district. While initially helpful, the robot seems to have a darker side as of Episode 19. After King Ren claims the shops in the server, Grian tries to get someone to act against him by rigging the random content generator that Grumbot controls. Later in that episode Grian returns, only to see a very angry Grumbot's face looking at him. After Grian apologizes, the machine responds with: "My Grian was sorry too". Season 9 Grian immediately freaks out because not only he has no idea what the message is referring to, but it would also imply that Grumbot did SOMETHING to the alternate Grian.
Grumbot gets even more unnerving when he reveals that Scar was the mayor, even stating that he was the best mayor… for about 5 seconds. Just what happened in Grumbot's version of Season 7?
... kaboom.