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In the first issue, it's revealed that the reason why Prisoner 777 is cooperating with Zim is because Zim has his kids held hostage and threatens to "erase them" if Prisoner 777 withholds any vital information.
According to Zim, GIR ate a baby at a hot dog place.
Issue 2 is actually kind of scary for the same reason that it's hilarious: just how far Zim will go to get at Dib, even in the most petty way. For once, we see a plan of Zim's go off perfectly (well, except for having no ride home, but he managed a way back by the next issue) and one can't help but imagine what he would be like if he managed to function like this all the time and not just when it was funny. Think about it: a normal Irken Invader is supposed to be able to conquer an entire planet of sentient, technologically advanced people all by themselves (albeit with the assistance of a SIR), and as we see with Skoodge they can accomplish that goal scary fast even against a formidable enemy like the Slaughtering Rat People. If Zim ever managed to keep himself on target long enough for a plan bigger than just thumbing his nose at his nemesis, humanity wouldn't stand a chance.
Issue 3's plot is pretty scary if you stop and think about it, as Zim's entire plan this time is to summon a Cosmic Horror to destroy the world and ultimately succeeds. Thank God for Negative Continuity.
In Issue 4, one of the Irken scientists has a PAK that is unlike one that was seen on the show... one that's filled with Vortian brains! This just raises all kinds of new Fridge Horror.
The cover of Issue 5, Gaz and Dib are on a couch in the middle of a destroyed city. Dib sits atop the couch screaming in horror while Gaz just sits staring at the reader while holding a controller, giving an unholy combination of a Death Glare and a Psychotic Smirk. No guesses for who's causing the destruction.
Then there's the actual story. Dib interrupted Gaz while she was playing a VR Game (as in turning the game helmet off) just so that he could get her to look at Zim yelling at a cat. So Gaz asks Membrane to build an invention that could allow her to enter alternate realities so she could search for a dimension that would allow her to take revenge on Dib for unplugging her game. After some searching, Gaz eventually finds a reality where gamers literally rule the earth and put non gamers in mind simulations similar to The Matrix where they are forced into the role of player characters, controlled by random gamers, and dying violently over and over. And Dib is kidnapped on her orders and subjected to this virtual horror. What's more frightening is that Gaz makes it clear that she's being merciful compared to how this process usually goes for non gamers by giving Dib occasional breaks between games - usually, it's just a never-ending nightmare for the "NPC".
Gaz offhandedly implies that she killed this reality's leader as well as its versions of Dib and Gaz.
In Issue 6, Zim uses a Borrowed Biometric Bypass at the bank for a fingerprint scan. Worse, when you note how decayed the hand looks, indicating that Zim's been carrying around for a while - where did he get it, and why did he take it in the first place if it wasn't for this?
In Issue 9, we find out what Zim does in his spare time to blow off steam — he goes to the Tiny Galaxy (that is, an entire miniaturized galaxy), takes in the joy and wonder of it all... and then punches a planet or two, for fun.
Seeing Zim goad Dib/Derb into crushing a planet is also quite creepy.
Earlier Zim also mentions that his last human test subject exploded. Considering the only test human subject seen on screen in the show in more then one episode was a boy named Nick, having not appeared in the comics so far, it makes for speculation...
Dib actually takes a dark side in this issue by not only allowing Zim to capture a hostile commenter but actually leads Zim to the guy himself! It also looks like the guy is not going to escape and going by what Zim said earlier he's pretty much screwed.
The commenter is actually back on by the end of the comic, which suggests he either escaped on his own or Dib might have released him after besting Zim.
Issue 12 shows what would happen if Zim ruled the Earth. For one, he forces all humans to wear helmets (resembling his visage) that electrocute if they disobey his orders or insult him. Then there's the fact that despite being a more "grown-up" version of the character, he's no less insane as his ultimate plan for the planet is to cut it in half so he can gift it to the Tallest as a snack bowl. Next, he "upgraded" GIR by giving him three heads, adding a T to the end of his name, and robbing him of his free will. Dib is long dead, having been captured and left to slowly rot away in prison with only an insulting mural of himself for company until he was little more than a skeleton. Lastly, the guy he ordered seat covers from gave him sleeves made out of hobo flesh and the only reason he's miffed about this happenstance is that they weren't lizard-skin like he wanted.
The back-up story, INVASION, also features a future where Zim is triumphant. And here, his reign makes for a much darker and twisted epoch.
Issue 21 has another one for Gaz; after being body swapped with Zim she uses his resources to make herself into a Villain with Good Publicity and takes over the Earth, some of her tactics include removing every weapon from the human race (making them believe it was for peace) and then poisoning the masses into submission (under the guise that the poison would stop world hunger).
Even setting aside the plot of the issue, the issue has a bit of an Art Shift compared to the usual, and the result is absolutely frightening. Gaz-as-Zim looks pants-shittingly terrifying, and Zim-as-Gaz ends up looking pretty unsettling themselves, though Dib and GIR swapping bodies makes for some good Nightmare Retardant.
Best part? The whole issue is in Negative Continuity and ends with Zim and an insane Dib stranded on the moon while Gaz rules the earth as Zim. None of them will ever get their bodies back, and even if they could, Dib's and Gaz's are likely permanently maimed.
Issue 22 sees GIR infected with a virus, which makes him try to kill Zim. Seeing the usually lovable robot going on a rampage is just disturbing.
Issue 34 brings in Moo-Ping 10, a private space prison where, if you have the money to pay for the service, your enemies can be locked up indefinitely. And in Zim's case, his "enemies" include random people he doesn't like, or who happen to look like people he doesn't like. While this is played for laughs, it's a pretty horrifying setup.
And if you're unable to pay the prison's bill, they lock you up. When this happens to Zim, he's tossed in with the people he had locked up (who specifically stay even when offered freedom, so they can have this opportunity), leading to him being repeatedly beaten up so badly that Toon Physics go into effect and reduce him to a wadded up mass of flesh.
Issue 39 gives us a reminder of how dangerously insane GIR is, as the alien scout Inquisitous plugs him into a memory viewing machine, which promptly overloads, causing Inquisitous' whole ship to explode. And then his superiors recover GIR and examine his memories to discover what happened, which apparently destroys their whole planet.
In Issue 40, one of the alternate universes depicted is one where everyone is nice all the time. And while this isn't disturbing in itself, there's the matter of this world's version of Gaz. She's so obsessively friendly that she'll force her friends to attend tea parties and sleepovers with her, even if she has to tie them up, gag them, and electrocute them if they resist. One could argue that this is scarier than her normal personality.
Issue 49 reveals that the Zimvoid isn't a Pocket Dimension, but all that's left of the home timeline of Zib (the alternate Dib pretending to be Zim Number 1). What happened to it? Somehow, his attempt to destroy the Irken Armada backfired, and destroyed the entire universe except that small bit of it. And worse, he's perfectly willing to attempt to repeat the process on other timelines in his mad desire to wipe out all Irkens in the multiverse, regardless of the risk of destroying those realities too. In his view, since there are infinite universes, it doesn't matter if he destroys some by mistake.
Zib himself is walking Nightmare Fuel material: A former alternate version of Dib who finally managed to capture Zim, but didn't get any respect out of it after all. Somewhere down the line, he got Zim's PAK attached to the back of his head, but unlike "10 Minutes to Doom", he survived being it's new permanent host somehow. Instead of this Dib having both his original personality and human body destroyed, Dib and Zim somehow merged in a similar vein to Dark Danny... with the PAK now visibly fused to his head like a tumor. The result? A twelve-year-oldHideous Worm Baby Irken Boy who possess all of the worst traits from both Zim and Dib, with absolutely none of their redeeming qualities. Maybe it's for the best of the entire multiverse that he's now stuck where he is...
Issue 50 echoes back to the Body Horror of "Dark Harvest", as Zim's newest plan is to harvest human brains so that they can power an Irken robot. So, we're treated to the lovely image of GIR carrying around a bucket that's literally overflowing with brains. And Minimoose somehow collected even more than him; when Zim questions how, his response is enough to shock Zim, which raises all kinds of questions.
The final issue has the existential horror of Zim and Dib being stuck in a "Groundhog Day" Loop forever. Dib tries many times to put an end to it, but no matter what he does the outcome is the same.
Gaz casually reveals that she'll periodically cut open Dib's head in the middle of the night and stuff things into it. The extreme close up of the back of his head showing the mass of scars and staples holding everything together, complete with blood still dripping from the latest (and biggest) cut, is deeply disturbing.
This is also mixed with Call-Back since Gaz did threaten to stuff things into Dib's head back in "Gaz: Taster of Pork" while he sleeps and apparently made good on it.
Considering Dib had no memory of the loop prior to the head incident, one could argue that she was attempting to save Dib's life in one of the loops. Makes you now curious as to what Zim did in the final Kill Dib route, assuming you don't want to sleep tonight...
, also features a future where Zim is triumphant. And here, his reign makes for a much darker and twisted epoch.