Mirror World

Lighthouse Keeper: I'll introduce you to... wait for it... the PARALLEL WORLD!
Huey: Um, how do I put this...? We, uh, already know about the parallel world. Weird pipe, right? Leads to a freaky opposite world?
Lighthouse Keeper: Oh... You already know about it... Well, yeah... the funky pipe leads to a parallel universe.

— Paper Mario: Color Splash

A level in a video game which is an altered version of an area you were in earlier. Sometimes you're visiting the same world in different time periods — be they separated by days, months, years, decades or centuries. Other times, you're visiting another version of the area in an Alternate Universe — maybe even a Bizarro Universe.

Such areas nearly always happen to contain Chaos Architecture, which "explains" why the Temple of Doom that you visited in the present day has a radically different floor layout ten years in the future.

May overlap with Dark World, might be used for Dual-World Gameplay. Not to be confused with Mirror Universe. Also not to be confused with Remixed Level, which is the exact same level with minor differences; this is an "alternate" version of the level, or one with intentional similarities.

If, however, the world is literally mirrored (i.e. flipped left-to-right), then it is a Level in Reverse. Likewise, a world that exists within a mirror (as opposed to the mirror itself merely serving as the gateway) qualifies for Pocket Dimension and/or Phantom Zone.

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Examples:

Action-Adventure

• The upside-down castle in Castlevania: Symphony of the Night.
• Castlevania: Harmony of Dissonance is somewhat similar to Symphony of the Night, except the player does not visit the second castle after visiting the first, but goes back and forth between the castles throughout the game, becoming aware of it around halfway through. The castle in which you fight the final battle helps determine which ending you get.
• Control has a mirror in Synchronicity Lab that leads to a mirror version of this place. It also affects Jesse's dialogue, but not her inner monologues. She has to fight an evil version of herself and what they break in this world breaks in the real Lab too.
• Done to great effect in Day of the Tentacle. The game's three protagonists are stuck in the same mansion, but one is in the present, one is 200 years in the past and one is 200 years in the future. A number of puzzles involve taking advantage of various objects that exist in the mansion in more than one time.
• In the old PC Adventure Game Dark Seed and its sequel, you point and click your way through the normal scenes in town, then go through a mirror to visit those places in a world designed by H. R. Giger.
• In Devil May Cry, the strange mirror where Nelo Angelo emerges from is revisited as a gateway in a later mission when Dante seeks the Philosopher's Stone. The mirror world is a more horrifying version of the real one, with a bloody color palette, tilted camera angles, and the entire screen also becomes distorted as everything slowly moves like a ripple in a water. It's also the place where you are introduced to the Nobodies, strong horrifying demons that can throw their eyeballs at you. Dante also notices that any object there is just an illusion because the Divinity Statue doesn't do anything.
• In DmC: Devil May Cry, most areas you move through in the "normal" Limbo City will transform into warped areas of the same environments in the "demonic" Limbo. At least once, the environment itself will be flipped 180 degrees, memorably in the approach to Bob Barbas' lair; the symbolism used for the transition depicts Dante moving to the other world through the mirror image reflected by the huge body of water.
• Illusion of Gaia's Sky Garden has you jump from the "right side up" portion of the garden to the "upside down" portion of the garden using "jump" points. Hitting certain switches has an effect on the obstacles on the opposite side. No real explanation is given on why, when you jump off a ledge, you don't fall off the edge and plummet to the Earth below (not to mention how you can walk upside down). It doesn't take away from the gameplay or story, though, so don't worry about it.
• Legacy of Kain: Defiance often had the two protagonists exploring the same locations while separated by five hundred years. The Spectral Realm may also qualify.
• The Legend of Zelda: A Link to the Past had the Dark World, where a puzzle required you to drain water from one world and use the fact it would fill the other.
  • The Legend of Zelda: Majora's Mask has the Stone Tower Temple, which you must flip from right-side up to upside down. Conditions in the "heads" version affect conditions in the "tails" version, and vice-versa.
  • The Past in Oracle Of Ages.
  • The future in The Legend of Zelda: Ocarina of Time. Certain actions such as planting seeds in the past have effects on the future timeline.
• Luigi's Mansion had the Hidden Mansion, which, in the PAL version only, was a mirrored version of the Normal Mansion made more difficult.
• Metroid Prime 2: Echoes: Dark Aether is a twisted, corrosive version of Aether, albeit occupying an alternate dimension. The layout and architecture is nearly identical in both dimensions, and the biomes are also similar (though much more polluted in Dark Aether). However, whereas Aether is inhabited by the friendly Luminoth, Dark Aether is inhabited by the aggresive Ing, and the latter world's atmosphere is very harmful for anyone who wasn't born there.
• Zack & Wiki: Quest for Barbaros' Treasure has one level in the Ghost House with a mirror, that hides the treasure from you. your mirror image is alive, and keeps moving it in between you going through tunnels.

Fighting Games

• Certain areas of Subspace Emissary in Super Smash Bros. Brawl have you shifting between daytime and sunset of the same level, using it to remove an obstruction — on both sides — from one side, that is indestructible on the other. It probably isn't a coincidence that this game and Kirby Super Star had the same designer.

First Person Shooters

• In the Marathon Game Mod Marathon EVIL, the penultimate level has a "5d space" portal which leads to a mirror version of the level occupying the same space.
• Doom mapsets:
  • Map 4 of TNT: Evilution, "Wormhole", has two versions of the same map which you swap between by going through a portal. However, you don't have to enter the Dark World equivalent to finish the level.
  • No End in Sight homages "Wormhole" with a map that has a Dark World and a deviously hidden third Darkest World.
  • Valiant has the secret level "Ghosts of the Old Kingdom"; the level is set in what looks like an Egyptian temple. By going through a portal you can move between the normal temple and its colorless, gray version which is inhabited by ghostly versions of normal monsters.
  • Going Down's map 5, "Time Warp"; you keep moving between the same laboratory in the present day and years in the future.
  • THT: Threnody's map "Parallel Dimension" has you travelling between two places with nearly identical floorplans, but one is a futuristic base and the other is a castle straight out of medieval fantasy.
  • My House: The entire map involves exploring multiple locations that, to varying degrees of subtlety, all seem to be variations of the same basic house template. A very literal version of this trope is accessed via the bathroom mirror, and is a completely inverted version of the house. A mirrored version of both Underhalls and the Gas Station can also be accessed from this area.
• Judge Dredd: Dredd vs. Death has an unlockable cheat which allows you to do this to the whole world.

Hidden Objects

• Alice in the Mirrors of Albion features a "Mirror World" map, which provides the player with an entirely new, but reminiscent, set of locations to explore, and quests to complete. The Mirror world has a slightly different gameplay from the original setting, and has a completely separate measurement for level, currency system and inventory items.

Platformers

• The four different seasons of Click Clock Wood in Banjo-Kazooie.
• Utilized in Braid, most Mind Screwingly in the final level.
• "Zoovania" in the Transylvania world in Bugs Bunny & Taz: Time Busters. If you visit during the day, it's a normal zoo. Visit at night and it's changed; most notably all the animals turn into monsters. You can toggle day and night from outside the zoo.
• Day and night versions of Fungi Forest in Donkey Kong 64.
• Haven City in Jak 3 has almost completely been taken over by enemies, but the layout of areas is the same as in the second game..
• Floria in the Kirby Super Star game Milky Way Wishes had you shifting between four seasons of the same level to get past barriers present during one season, but not another.
• In La-Mulana, almost all parts of the ruins had a "front side" and a "back side." One set of front and back areas in particular is the Twin Labyrinths, an area whose front and back side are mirror images of each other.
• A 3D game based on Phineas and Ferb The Movie: Across the 2nd Dimension has the playable characters going through two dimensions on each level.
• A major part of Prince of Persia: Warrior Within takes place in a ruined fortress both in the present and the past. You will often need to travel between the times to find away around obstacles.
• World 6 in Purple is a set of five (not including 6-6 and Final Destiny) stages replicating the looks of previous worlds with neons. Stage 6-1 is an almost exact copy of stage 1-1.
• Ratchet & Clank: Up Your Arsenal has an actual Mirror cheat. Levels can be played as mirror images of themselves.
• Sonic the Hedgehog CD's Past, Present, Bad Future and Good Future versions of the same levels.
• A lot of the Special Levels in Super Mario 3D Land.
• Super Mario 64 had Tiny-Huge Island, in which you could enter pipes and travel to the other world. Everything was exactly the same, save for size.
• Subspace from Super Mario Bros. 2.
• Super Mario Bros. 3 has a level with doorways that lead to a mirror version of that level where the enemies are normal-sized (normally they're huge because the level is in Giant Land)
• Flopside in Super Paper Mario is very literally a mirror world: you get to it through a mirror, and it's a reversed version of the first town. The people are even the opposite of the people in Flipside. For example, Flipside has a grandmother who gives good advice, which her granddaughter says she is following while doing just the opposite, while Flopside has a grandmother who gives bad advice, which her polite, obedient grand-daughter is willing to follow.

Puzzle Games

• In Lara Croft GO, the Mirror of Spirits downloadable expansion features levels in which Lara's world comes parallel to a world of spirits, containing a mirror Lara. This alternate Lara makes exactly the same moves as "real" Lara — but the spirit world isn't quite an exact clone of the real one. This results in simultaneous Dual-World Gameplay, with players having to find moves which work in both worlds rather than just one of them.

Racing

• Mario Kart has had Mirror Mode since Mario Kart 64.
  • Diddy Kong Racing does this as well in Adventure Two; all tracks are mirrored.
• The first three circuits in LEGO Racers are a series of creative tracks based on various Lego themes, with each track having a specific character to represent it and a champion somehow connected with the theme of the first track representing the circuit overall. Then the next three circuits are the exact same racetracks as before, but in reverse order and mirrored, with the champion racer being connected to the theme of whatever track was previously last.

Roguelikes

• The Binding of Isaac: Repentance has two variants:
  • Downpour/Dross II has a literal world inside of a mirror where all the rooms are reversed. Knife Piece 1 is found here, a copy of the floor's boss can be fought for an extra boss item, and the shop, curse room, and other special rooms are all empty.
  • Just before reaching The Very Definitely Final Dungeon, the player has to go through remixed versions of the previous floors, in reverse order. Starting from Caves/Mines II, much stronger versions of the enemies from the floor will appear, bearing the armor normally reserved for superbosses and complex attacks.

Role Playing Games

• The entire world in Dark Cloud 2. The world you enter by going through the red Time Gates is the same world you're already in, but 100 years in the future. Since so much time passes, the differences between the two can be...striking.
• Amaterasu Server in Digimon World 3.
• Dragon Age: Origins has a few different examples of this, depending on which origin the player chose. Dwarf nobles, dwarf commoners, mages, and city elves will all revisit their homes about one year after they left and much has happened in the interim, while Dalish elves will revisit the same forest they grew up in, but with a different clan of Dalish after their own clan left.
• EarthBound (1994) has Moonside, which is a twisted, alternate reality version of Fourside.
• Neverwinter Nights had a temple that you had to enter in the past in order to fix something in the present. You went in in the present, found a way to the past so you could change something, then went back in in the present and your problems were solved.
• Neverwinter Nights 2: Mask of the Betrayer combines this with Dark World, launching the player into Shadow Plane versions of some locations in the main world.
• The Caverns of Time in World of Warcraft are basically this trope mixed with Time Travel. You travel to past versions of some in-game zones and dungeons to witness major lore events. They are mostly an homage to earlier games in the Warcraft franchise, but the latest bunch added in a Cataclysm content patch are integral to the main plot.
  • Warlords of Draenor adds Draenor, which is The Burning Crusade's Outland before the planet exploded. Draenor was previously visited in the RTS Beyond the Dark Portal, but a lot has changed since then.
• Nightfallen Jahai in Guild Wars is a dark, Realm of Torment version of the Jahai Bluffs zone, with the same shape (including zone entrance locations), but terrain types and inhabitants appropriate to the Realm of torment. It is implied that this is what the real Jahai will be like if Nightfall occurs (which the players are trying to prevent.)
• Paper Mario:
  • In Paper Mario the other side of the Crystal Palace looks like another world in the mirror, but while things on one side affects things on the other, it's not an alternate realm. Duplighosts are just messing with Mario. Get rid of them, and it becomes clear it's just a castle with near-perfect symmetry separated by a glass (or ice) wall.
  • In Paper Mario: Color Splash, all sorts of strange phenomena happen on Prism Island's northwest sector, especially the islands off the coast. Much of this can be traced to the Parallel World, an alternate reality that Mario can enter through special Warp Pipes in the middle of glowing magic circles. The Parallel World's enemies are significantly stronger than the Normal World's (though nothing Mario can't handle), the ocean is missing, and the colors are incredibly strange. Played for Laughs, however, when Mario finds the source of some of these phenomena: The whirlpool that never goes away is actually an extremely long spin cycle from a washing machine at its location in the Parallel World, and the smoke coming out from seemingly nowhere is actually coming from a Toad in the Parallel World barbecuing some fish.
• In Star Wars: The Old Republic, Republic players visit Taris early in their storyline, where the Republic is trying to rebuild it after the catastrophe from centuries earlier. Imperial players go there a few chapters later to undo the Republic's work and keep the place an uninhabitable hellhole. Notably, the Imperial chapter is set at night, giving it a Dark World feel.

Survival Horror

• Eternal Darkness is 12 levels long, which is to say it's four areas set in different time periods, led by different characters, with different obstacles\items\enemies\routes\etc.
• Ghost Hunter has two different versions of the DeMontford Mansion. There's a Weird version and an Evil version, so named in the save file titles. There's also a normal version, but only a few rooms of it are visited.
• In Penumbra: Black Plague, you visit a darker, much creepier version of the very first area in the first game, "Penumbra: Overture"

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