For That Lovely, Lustrous Beard
Star Trek and the Mirror Universe
Ah, the Mirror Universe, a classic trope of sci-fi storytelling. You can find versions of this in just about every media, from television to comics and novels, too. Of course, the term itself comes from Star Trek. In the episode "Mirror, Mirror", Kirk and his crew accidentally end up in a parallel universe. Although the characters never call it a "mirror universe", that's the name that stuck from the episode title.
So what makes a Mirror Universe? Well, within the confines of Trek, the Mirror Universe is dominated by dark, aggressive versions of the characters we know, working in service of an empire (Terran at first, and then an collective of alien races later). In this version of the universe Diplomacy gives way to Domination, where peace is never as important as war. For a series like Trek, a dark versions like this illuminates the goodness of the "real" characters and highlights just what we like so much about the people we know.
That's what makes parallel universe stories like this so compelling: the knowledge that with just a few small changes to history, our lives could be very different. We could be very different. The ability to explore that for a short while, to see just what makes us who we are versus what comes about because of our environment, leads to compelling stories. Parallel universes are an intriguing concept and, because of it's history and willingness to occasionally check back in and explore it's own Mirror further, Trek is uniquely situation to truly delve into the concept.
So let's do just that and delve into the classic Mirror Universe episodes of Star Trek:
The Original Series, Season 2, Episode 4: Mirror, Mirror
The Enterprise is on a mission at Halkan, a peaceful planet with reserves of Dilithium but no desire to let the Federation mine the planet. Striking out, Kirk, Bones, Scotty, and Uhura beam back to the planet, but an ion storm disrupts their beaming. The quartet find themselves beamed to the Enterprise, but at the same time not their Enterprise. They find themselves in a parallel universe, one where humans are savage warriors, and the Federation has been replaced with the 4erran Empire. The crew will have to figure out what happened and how to return all while blending in to the crew. Oh, and they have to avoid getting killed by all the lower-ranked officers looking to assassinate their superiors and move up in rank.
When it comes to Star Trek episodes (not just from The Original Series but overall), "Mirror, Mirror" may be the most famous of them. Certainly it's one of the most popular, and it's easy to see why as this is a compelling hour of television. Since we're already well familiar with the crew of the ship, having spent, by this time, over a year with them, watching their exploits, the episode is able to show us a dark, evil version of the crew that seems so strange to us because of our knowledge of the "good" versions. And episode like this only works because of that familiarity, that knowledge of who they should be contrasted with how they're acting in this darkened mirror.
There's a dark fun to watching Kirk and the rest try to move about the ship, dodging dangers that lurk around every corner. This is aided, in no small part, by the fact that Shatner was clearly enjoying this version of the show -- there are so many scenes of Kirk stumbling into yet another plot on his life where Shatner has this little grin on his face, this look like, "hey, what fun this mirror universe is." He is the lead of the adventure here, with this episode being much less on an ensemble piece just by the way the story plays out. It's a good thing, then, that Shatner was giving this episode his A-game, really reveling in the story while providing the proper level of charisma and bombast needed for it.
Nimoy, too, seemed to enjoy being able to perform his characters, both the Mirror Spock confronted with these odd versions of the people he knows, and the good Spock dealing with the mirror versions of his Captain and crew. Hell, really, everyone involved seem to have a thrill with it, including Sulu and Chekov in this vile, evil forms. Shows don't always get to explore the deep, dark evil of their protagonists, but an episode like frees the writers to really delve, and it frees the actors to bring out new sides of their performances.
Which brings us back around to my original point: an episode like this only works because it's already spent the time earning it. We know Sulu and Chekov, so seeing their evil versions has real heft to it. if this had been the second or third episode of the first season, the impact wouldn't have been the same. The episode is great, but it so good because it's put the time an effort in with the characters and the world-building to be able to pull off a story like this and stick the landing.
- "Your agonizer, Mr. Kyle." "I left my ex-wife back on Earth. Heyo!" *pulls at shirt collar*
- Man, Uhura has some toned abs.
- Yeah, scream, Chekov! Scream!
- There Kirk is, once again getting all the ladies.
- For a guy with fencing training, Mirror Sulu really sucked with a knife.
The Original Series, Season 3, Episode 9: The Tholian Web
When answering a distress call from the USS Defiant, the Enterprise discovers the ship floating in space, glowing with a green light. Kirk, Bones, Spock, and Chekov head over to the ship to find out what happened, only to discover that the crew had mutinied, killing each other. While exploring the Defiant, soon the crew begins to realize that the ship is literally dissolving around them. Due to fluctuations in the fabric of space around them, the Enterprise suffers degradation to her power, thus forcing Scotty to limit how many of the crew of the team he can beam back. Kirk stays behind to be transported after the rest, but between the crew moving over and Kirk's beaming, the Defiant disappears, seemingly taking the captain with her.
Soon after, a Tholian ship arrives on the scene. Unwilling to wait for the Enterprise to save her captain, the aliens become aggressive and begin to build a capture web around the ship. Spock had to lead the crew, save the captain, and find a way to escape the Tholian Web (title drop) before the Enterprise is captured forever.
I had heard that the third season of The Original Series was pretty dire, but I expected this episode to be pretty decent -- it was referenced in the Mirror Universe episodes of Enterprise, after all. Surely an episode with renewed legacy would be pretty good. While the aliens are certainly interesting, and the web they construct is a neat concept, the episode on the whole is a total drag.
For starters, while the threat of the Tholian Web is certainly explained to us by Spock, we never really see any consequence of it. Was the Defiant captured by the Tholians and that was what caused that ship to phase in and out before disappearing? Would the web do anything to the Enterprise? Is it related to the crew members slowly going mad, or is that something else in that sector of space? More questions than answers are forthcoming, and instead of explaining everything to us at some point, we mostly just watch the crew of the ship stand around and wait. That does not make for thrilling television.
I will credit Nimoy in this episode as his performance as the cool, calculating Spock and fantastic here. The one person on teh ship keeping his act together, Spock is the real hero here. DeForrest Kelly, though, overacted his role, coming off as way to aggressive towards Spock, making it seem like he couldn't trust him, as if they hadn't spent over two years together on the ship learning each other. As great as Spock was, Bones totally sucked here.
The concept of a episode without Kirk is great, as is the Enterprise getting caught in a trap of unknown origin. The story in and around these details, though, is just bad. A forgettable episode that no one would watch again were it not specifically referenced in the later, "In a Mirror, Darkly" episode of Enterprise (which is, of course the only reason why I watched it in the first place). If the rest of third season is like this episode, I was right to skip it.
- Kirk and the away team wear actual space suits when going over to the Defiant. I thought the enviro-suits were just gray sashes or sometimes fancy vests. So inconsistent.
- "Has there ever been a mutiny on a starship before." "Negative, ensign." Well, Discovery really screwed this pooch.
- It's a Mad, Mad, Mad, Mad Chekov.
- Damn, they gave up on Kirk rather quickly.
Deep Space Nine, Season 2, Episode 23: Crossover
While The Animated Series and Next Generation skipped doing anything with the Mirror Universe (at least on television -- we'll get to comics and novels in a bit), Deep Space Nine made several voyages into the darker world, and it all started with the second season episode, "Crossover".
Venturing back from a mission in the Gamma Quadrant, Major Kira and Doctor Bashir suffer some plasma issues on their runabout right as they're advancing into the wormhole back to Deep Space Nine. The plasma leak causes the ship to crossover into the Mirror Universe, although the two officers don't realize it immediately. Immediately upon exiting the wormhole, the runabout is confronted by a Klingon bird-of-prey and taken back to the space station which is back in orbit over Bajor (as our side's station was at the beginning of the series). There the two officers are confronted by mirror versions of their own crew, including the Intendant, an evil version of Major Kira. The intendant takes a shine to her mirror version, but Bashir is case into the ore processing mines. From their two places aboard the station, Kira and Bashir have to find a way to get back to their ship and make it home again.
As with the original "Mirror, Mirror", what works in this episode is seeing versions of the characters we know that don't act anything like we'd expect. The trick is, though, that while these characters act different, darker even, they aren't the barbarous warriors that imperial Terrans were back in the Original Season episode. The implication, thus, is that while the universe may be darker, it's not because everyone is inherently evil by design. People can be good, sides can be swayed, and maybe everyone could be redeemed if they just tried.
Of course, there's the contrast of the fact that, as we're told, when Mirror Spock took over the Enterprise (as the insistence of our Kirk) and then, eventually, became leader of the whole Empire, he then weakened the Empire with his reforms, allowing the Klingon-Cardassian Alliance to defeat them and take over. Sadly, the Alliance really isn't any better than the Empire was, at least when it came to the treatment of the Terrans. Some could argue that the Alliance is cruel to the Terrans after years of being oppressed by the Empire, but that doesn't change what we see. The Terrans here are pitched as the oppressed, the good guys we should care about, and the Alliance is little better than the Empire -- cruel, barbarous, and almost savage.
So while it seems like the Mirror Universe people can actually be redeemed, it's almost like the episode also undercuts that message. People betray each other all the time here, and maybe that's just because that's how it's always been done in this universe or maybe it's baked into their very nature. It's hard for a single episode to delve that deeply into the subject, especially when it wasn't expected that the episode would have any follow tales in the series. On it's own, the lack of hope, the fact that when people try to reform the way things are they inadvertently makes it work, that then makes the Mirror Universe seem even more cruel than it was before.
I like this episode for what it is, an interesting look at the characters we know so we can see them in a new light due to differing circumstances. But because the Mirror Universe is still segregated from the main continuity at the end of this episode, it's hard to call this a great episode. It's an interesting tale, but seemingly has little impact on the overall story of Deep Space Nine.
- I still feel weird rooting for the Terrans after how bad the Empire was. Sure, it's sucks for the humans, but they weren't any better when they were in charge.
- Oh, Avery Brooks. You do so love to go broad in your performances. Leave a little of that scenery for everyone else, otherwise you're liable to chew it all.
Deep Space Nine, Season 3, Episode 19: Through the Looking Glass
While taking care of routine business on the station, Sisko is interrupted by O'Brien who has a personal matter to discuss. Suddenly, O'Brien pulls a phaser on the commander and drags him over to a transporter. The two beam over to O'Brien's ship which, we learn, is in the Mirror Universe because this is the Mirror O'Brien (aka Smiley). Smiley needs the commander's help -- the Mirror Sisko was recently killed on a mission, and if Sisko Prime doesn't help out (by taking the place of Mirror Sisko) the mission goes tits up and the Terran rebellion against the Alliance goes with it. The mission: get back onto the Mirror DS9 and "rescue" Mirror Sisko's wife, Jennifer, before she can finish building a sensor array for the Alliance that would expose every rebel ship and base across the quadrant. Sisko will have to finish this mission to save the rebels (and earn his way back home).
The episode starts kind of slow, although I think part of that is because it's still so hard to root for anyone in the Mirror Universe. The Terrans were jerks back in the span class="tilt">Original Series era, and everyone else is a jerk now towards the Terrans, so why should we really care? It doesn't help that every Terran we meet in this episode is a ruffian, a no good dirty fink that would populate the background of any evil gang in some other episode. They aren't the kinds of people we're going to consider "heroes", basically.
But then, all because of Avery Brooks and his performance as Sisko, the episode suddenly gels together. Sisko ends up on the Mirror DS9, starts being the most charismatic scalawag you've ever seen, and you just can't help but enjoy the episode all of a sudden. This is one of those times where Brooks's over-the-top performance style works so well in the series -- he carries this episode and makes a fairly rote storyline into a really charmer.
Don't get me wrong: I'm still not so certain if rooting for the Terrans is the right thing to do here. Who's to say that they won't just become the evil dick-heads of he universe once they're back in control? For now, though, this one episode sells the idea of regular visits to the Mirror Universe better than anything the franchise has done so far.
- So we see Mirror Dax (not Mirror Jadzia but Mirror Dax), Mirror bashir (presumably without all his genetic enhancements, but who knows), Mirror Tuvok, and Mirror Rom this time around. All these people that have business in and around the Gamma Quadrant in the Prime universe also apparently congregated here in the Mirror Universe. I know the cast of the show is only so big, and the producers wanted to give every principle cast member time in the episode, but considering the vastly divergent history between the two universes over the last 100 years, it stretched credulity that all these people would end up here, let alone that they would have all been born.
- It's complicated further when you realize that Mirror Sisko and Mirror Jennifer didn't have a kid, but the Prime universe versions did. So sometimes people don't get born in both, but not always? Someone will have to explain the rules of this to me at some point.
Deep Space Nine, Season 4, Episode 20: Shattered Mirror
When Jake comes home to his shared quarters with his dad, Sisko, he sees his mother, Jennifer, sitting in the room. He's shocked, of course, but the woman quickly reveals herself to be Mirror Jennifer (who we met in the last Mirror Universe episode). The two bond and have a great time, so Sisko leaves them in the quarters while he goes off to do some work. When he comes back, though, he finds them gone, and a Mirror Universe transport device waiting for him. Quickly, he beams over to the other universe and gets sucked into their mess once more. They have their own version of the Defiant built, but they can't get it to work right. They need Sisko's help to finish the ship before the evil Alliance comes back to Mirror DS9 and kills every last Terran on the station.
Well, it's not tradition. Deep Space Nine was going to do one of these Mirror Universe episodes just about every season now, so that's why we're back at the well again. I do appreciate that it's not the same exact story as before -- instead of getting trapped in the MU, or having one of the Starfleet officers pretend to be their Mirror counterpart, Sisko just gets to go over, help out, and leave. Everyone knows who he is, which version he is, so there's no mistaken identity or subterfuge. That's refreshing.
What isn't so refreshing is the fact that to get the help for their Defiant the Mirror Universe Terrans essentially kidnap Jake first and then Captain Sisko after. We already had this plot detail in the last episode, "Through the Looking Glass", and since Sisko has already proven himself to be willing to assist the Terrans once in a while, maybe they could have tried asking first instead of just resorting to kidnapping? Sure, Sisko says he would have said "no" if they had asked, but that's in retrospect when he was already kidnapped and raging mad, so obviously he was in no mood to help at that point.
Put another way, the Terrans still have yet to show how they would be better keepers of the Mirror Universe than the Alliance or anyone else. Everyone on that side seems to be a jerk, resorting to dirty tricks, violence, and torture to get what they want. No one seems like a good person, no one seems worth saving. It's hard to say why we should care at all about any of this when, once Sisko goes back home, everything is going to descend into chaos once more.
So maybe Sisko was right. Maybe helping these people really is a lost cause. Huh...
Overall, this was a middling episode that even Avery Brooks's Sisko could really save. The story acts like a footnote to the previous episode and never really justifies its own existence. Put another way: if the Terrans hadn't needed Sisko's help with the Defiant, would they have ever bothers showing up gain at all? That's not a great place to start your episode from, and the episode is never able to recover from there.
- Oh look, the Captain has been kidnapped by the Mirror Terrans again. And these are supposed to be the good guys?
- Hey, Mirror Worf. At least him being around makes some kind of sense.
- And Jennifer is dead in this universe, too, now. That seems fitting.
Deep Space Nine, Season 6, Episode 8: Resurrection
Speaking of dud episodes, now we get to where the Mirror Universe really falls off in Deep Space Nine. In "Resurrection", Dax and Kira are working in Ops when someone makes an unauthorized beam-in. Kira is shocked when the person turns out to be her dead lover, Barrel, and it's even more shocking when he pulls a gun on her and takes her hostage. As it turns out, this is the Barrel from the Mirror Universe, and he's on the run from everyone on the other side. Kira disarms him eventually but elects not to press changes, instead striking up a kinship with the man. Soon they're spending all their time together, bonding and becoming more than friends. But there's more going on with Mirror Bareil than he's letting on, which becomes clear once the Mirror Kira shows up. The two are on Deep Space Nine to grab one of the Orbs, treasures from the Prophets, and Kira will have to figure out their plan and stop them before they make off with a power treasure.
After three Mirror Universe episodes, DS9 took a year off, with no new MU episode in season five. That could have been a good thing as it would allow the producers to come up with fresh, new ideas for the MU without overdoing things or letting them become stale. Unfortunately, the episode they came up with is one of the most boring of DS9's run. Very little of consequence happens in the episode, and then just as suddenly as Bareil appears he whisks away never to be seen again. It's all so dumb and pointless.
Of course, it would have mattered more if Mirror Bareil didn't show up for just a single episode. If he could have appeared and hung around for half a season (with other A-plots going on in the foreground) before his heel turn occurred, that would have actually had some impact. Instead, from the moment he shows up he is the A-plot, and thus we're waiting for the other shoe to drop the whole time. His heel-turn doesn't matter because it was expected. So he shows up, goes bad, and leaves. Who cares? It has no bearing on anything going on in the season which, remember, includes the Dominion War. Up against that major plot line, a visit from Mirror Bareil is just not worth the effort.
Plus, to be frank, Bareil is boring. He was boring in his original form and he's just as boring here. The blame for that has to lie with actor Philip Anglim. He never invests anything close to charm or charisma in the character which, really, was a problem with both the original Bareil and the Mirror version. He's an empty void of a performance when a character like this needs some soul, some gravitas. If the character had been played by someone else then sure, maybe this episode could have worked better. We'll never know, though, because the Bareil we get sucks.
In the end the show would have been better off just focusing on the Dominion War for another episode instead of taking time away for this pointless diversion. This episode only serves to show that we really don't need to keep visiting the Mirror Universe over and over again. That said, this isn't even the worst Mirror Universe episode of Deep Space Nine's run. Oh no, that comes next...
- Every time they say "orb experience", it sounds dirty.
Deep Space Nine, Season 7, Episode 12: The Emperorís New Cloak
We start with Quark, in his bar, watching Ezri Dax (new host for the Dax symbiote after Jadzia died at the end of last season) and Dr. Bashir on a date. Apparently Quark has a thing for Ezri, something that isn't reciprocated. His musings over a future with Ezri are interrupted by his brother, Rom, who comes running in to warn Quark that the Grand Negus, the leader of Ferengi culture (and finance, of course), has gone missing. Not thinking much of it at the time, Quark goes home, only to find Ezri at his door, a knife in her hand. Naturally, this is the Mirror Ezri, and she tells Quark that the Negus is being held on the other side, by the Alliance Emperor. Quark and Rom has to steal a cloaking device and bring it across the divide to free the Negus But, of course, capers like this are never that simple...
This is, without a doubt, the worst Mirror Universe episode in the whole run of Star Trek. Ferengi stories on their own aren't all that interesting -- they're an entire race of underwritten, half-baked caricatures. Any time Deep Space Nine devoted time to the Ferengi, the entire series ground to a halt. Sure, they're funny in small doses, but these were never characters that should have been given episodes of their own (no matter how good Armin Shimmerman was as Quark).
By giving the Ferengi the lead in a Mirror Universe episode, the series plays to two of the worst trends in the run: Ferengi-centric episodes and and round of Mirror Universe shenanigans. As I've been saying for the last couple of episodes, the Mirror Universe is played out, especially when it comes to how Deep Space Nine was handling it. Nothing in the MU has consequence on the main continuity, and considering the fact that the series was still dealing with the Dominion War, even in season seven, taking time away for this a story set on the other side that won't, in any way, influence the main continuity, that's a real waste of resources.
Plus, making the Ferengi the center of a Mirror Universe story renders the MU a comedic farce. This is supposed to be a version of the Star Trek continuity where everyone is at their worst, ruthless and evil. To make it comedic violates that whole conceit. What's the point of the Mirror Universe if it's not going to shine a spotlight back on ourselves. What does humanity learn from a comedic episode about Ferengi on the other side? Nothing. It's just stupid.
I guess the best thing that can be said about this episode is that it's the last Mirror Universe story in the main Deep Space Nine run. Thank goodness for that.
- I have nothing to note here. This episode was so boring I didn't even bother taking any notes about it. Nothing good, or amusing, or interesting happened. Stupid Ferengi.
Enterprise, Season 4, Episodes 18 & 19: In a Mirror, Darkly
And finally we reach the last of the Mirror Universe episodes before Discovery took over. Unlike previous episodes, these two take place entirely in the Mirror Universe, so instead of having our heroes wander over to the other side and act all shocked by what they see, we get to fully experience the MU in all its glory. An interesting idea, to be sure.
The Empire is at war with an alliance of alien races... and they're losing. They need a miracle if they're ever to conquer their foes and, once again, expand across the universe. Commander Archer (not Captain over here) thinks he has the perfect solution: a mysterious ship, trapped in Tholian space. The only problem: his captain doesn't agree with the assessment and refuses to head into that region. So Archer stages a coup and takes over the ship, promoting himself to Captain (as is the way in the Empire). He sends the Enterprise to Tholian space only to discover the U.S.S. Defiant, a Federation ship from another universe... and also 100 years from the future (events alluded to in "The Tholian Web").
Archer immediately sees the potential for this ship, a bigger, stronger, more technologically advanced ship than anything the Empire has access to. After a skirmish with the Tholians, Archer takes over the ship and immediate sets about plans to become the new Emperor. But he'll need to watch his back as there's always someone waiting to dethrone the captain, especially when there's a prize this big on the line.
Make no mistake, a set of episodes set entirely in the Mirror Universe has strong potential. Since we're not seeing this universe from the eyes of the normal characters, we don't have to worry about the implications of this episode on the larger, main continuity. This was a problem Deep Space Nine never managed to address no matter how many times that show went back to the Mirror Universe well. Enterprise nicely side-steps that problem, making for a better couple of episodes.
And that's not to say "In a Mirror, Darkly" doesn't have an impact on the larger continuity. The implication of these two episodes is that, if not for the Defiant and her powerful tech, the Empire would have fallen into ruins years earlier. Instead of being just a bunch of rag-tag humans, the Empire used the tech on the Defiant to lead light years ahead of everyone else and, by the next time the Federation encounters the Empire, the Mirror Universe side is even more powerful. There are implications with this episode that were the two universes to ever come to blows, the Empire would have the upper hand, all because they cheated when they got a hold of the Defiant.
From those angles this show works. The problem, though, is that none of the cast is really good at playing these kinds of evil characters. None of them have the panache for evil that Nana Visitor's Intendant Kira or Michael Dorn's Emperor Worf had. It takes a solid actor to not only shake off the mannerisms of a character they've played for years but then invest in a very different version of them for a single story. Not everyone can do it, and no one in Enterprise was really up to the challenge. It's sad, because this flaw holds the episodes back from being great. It's still a good story, it just could have been even better in the right hands.
Still, "In a Mirror, Darkly" gets an A+ for effort. It sends the Mirror Universe off in style... at least until Discovery mucked it all up.
- I like how not only did they re-cut the climactic First Contact meeting (from Star Trek: First Contact) between the Vulcans and the Humans so that the Humans kill the Vulcans and take over their ship, but the episode also has a re-cut intro credits with scenes of war (instead of exploration) and darker, less poppy music. Nice touch.
- Scott Bakula is a good actor, but damn does he suck at being a tough-as-nails Empire soldier. He just doesn't have the cajones for it.
On the whole, the Mirror Universe is a concept that's better on paper than in execution. The idea of an evil version of the universe is powerful and helps to shine a light on our better selves, as well as our darker, baser instincts. As a one-off story, the Mirror Universe worked, but it's rare that any of the follow-up episodes were able match the gut-punch concept of the original "Mirror, Mirror" episode that introduced the universe.
Of course, the Mirror Universe is a fan-favorite idea, so it's doubtful that Star Trek will ever let the concept die.
More Mirror Magic
While this article is an overview of the Mirror Universe in previous versions of Trek, it doesn't take into account anything happening in Discovery. The entire first season of that show, essentially, had ties to the Mirror Universe (ties we won't spoil since Discovery is still new). It all was capped by a big venture into the MU for a set of episodes. Even now, one of the Mirror characters is still in the main continuity, which could have implications for the series moving forward. But then, that's all too much to recount in detail for an article such as this.
If you interest in Star Trek verges into extended universes, though, there are plenty of tie-in products you can check out as well. Between "Mirror, Mirror" and "Crossover", Next Generation had it's own Mirror Universe adventure in the Diane Duane novel "Dark Mirror". In this story, the Enterprise D is pulled into the MU by the I.S.S. Enterprise. There's a plot by the Empire to steal the ship, take it over, and use it as a stepping stone to moving into Federation space and conquering that territory as well. The novel is decent enough, but it was immediately ejected from potential continuity the second Deep Space Nine did it's own twist on the MU.
Of course, that was only one of a number of novels that have been produced for the Trek extended universe. There's the Glass Empires saga, three novels showing the evolution of the Mirror Universe from ENT (post "In a Mirror, Darkly"), TOS (post "Mirror, Mirror"), and TNG (in the "Crossover" continuity). There's also the Obsidian Alliances saga, a companion set of three novels following DS9, VOY, and the characters from the New Frontier novel crew. Plus, as a final companion, there's "Shards and Shadows", a collection of short stories set in this same continuity. And then they just kept making books in the set. Seriously, you could spend a long time just reading Mirror Universe novels.
After that, you can start getting really deep into the weeds. William Shatner wrote (or, really, had ghost written) a set of novels featuring characters from the Mirror Universe. it's all a flimsy excuse for him to bring back Kirk after that character's death. They're also all, unequivocally, bad novels.
There's also Dark Passions, a set of two Mirror Universe novels focusing on female characters from the other side. While that idea is commendable, certainly, these books look like trashy romance novels. If that's your thing, I suppose you could do worse.
Lest you think the Original Series movie continuity was beyond Mirror Universe shenanigans, DC printed an eight issue mini-series, The Mirror Universe Saga following Admiral Kirk as he battled with his Mirror counterpart for the fate of the universe. This mini-series is actually pretty well loved by fans, and has been reprinted a couple of times, so if any MU extended material might hook you, I'd encourage you to check this one out. And then later IDW followed up this run with a three issue set, Mirror Images, if comics are your thing.
And, of course, that doesn't even get into various video games, like Shattered Universe, Elite Forces, and Timelines, also dealing with the MU. Plus the Trek Collectible Card Game had Mirror Universe expansions and Decipher released the MU expansion Through a Glass, Darkly for their beloved tabletop RPG. In short, I doubt you could ever keep up with all the extended Mirror Universe materials even if you wanted to.