Underground Monkey



"Skywarp: At least I'm not ugly.

Thundercracker: Ugly? You and I look the SAME!"

- Transformers: War for Cybertron

Sprites and textures are expensive. Original ideas for monster types are even more so. As a result, there is a tendency to keep the number of distinct enemy types small. In an RPG or similar game where the player is expected to become more powerful over the course of the game, this is a problem, as the monsters stop being challenging about the time you Get on the Boat.

The solution many games go for is to have a small set of monster types, but have them appear with different graphics. Often, this change of design will be accompanied by a new adjective to go with their name (if the monster was based on a mythological or cryptozoological creature, subsequent names will be alternate names for the creature (Bigfoot to Sasquatch to Yeti), or the name of a similar creature (Cockatrice to Basilisk)). Typically, all such monsters will be vulnerable to the same strategy, or a variation thereupon, but later colors will tend to be more powerful. Elemental variations are a common version of this trope as are variations in size and adding or removing features like horns or wings or crowns.

Underground Monkeys are often Palette Swaps, meaning only the colors change but models are recycled, but they don't have to be. As long as they're recycled versions of previous enemies, the changes between the different versions could be anything. You might have normal Goombas, winged Goombas, spiked Goombas... Even King Goomba is a type of Underground Monkey.

Results in the somewhat strange phenomenon that as you travel a diverse world, rather than seeing a diversity of creature types, you see the same creature types, in a diversity of versions: in The Lost Woods, you find the Wolf, the Giant Rat, and the Forest Dragon; in the Slippy-Slidey Ice World, you find the Arctic Wolf, the Snow Rat, and the White Dragon; in the Temple of Doom, you'll face the Dire Wolf, Plague Rat, and Zombie Dragon.

The most common Underground Monkeys are those whose names begin with one of fire, ice or lightning. In games which play Elemental Rock-Paper-Scissors, the colors may also indicate elemental weakness.

Named for a Running Gag in RPG World, wherein the Underground Monkey is suspected of being attracted by Genre Savvy characters.

Action-Adventure Games

 * The Legend of Zelda also produced several colors of its major enemies, indicating their strength. Versus Books' Strategy Guide for Majoras Mask characterized the White Wolfos as being "like regular Wolfos, only, um, whiter."
 * The Bad Bat is an outdoor version of the Keese.
 * Keese themselves come in several elemental varieties in the 3D titles. Along with regular Keese, there are Fire Keese, Ice Keese, and as of Skyward Sword Thunder Keese and Cursed Keese.
 * The Wind Waker and Twilight Princess avoid this with every enemy except for Darknuts, whose armour changes colour to indicate different levels of strength, and the various Chu types, the Zelda take on the classic slimes. There are some minor palette swaps as well, but these take the form of giving the enemies extra armour and better resistance to the player's special attacks.
 * In the Oracle games, most enemies come in red and blue, indicating respectively a better attack and a better defense. This and various other instances of palette swaps throughout the series are nods to the very first game's use of two palettes for most enemies, usually a red/orange palette and a blue palette, where one would take more damage to kill than the other.
 * In Spirit Tracks, there are five types of rabbit you can collect, matching the environment in which they're found, including one that lives in the sea.
 * Chu-Chus in Twilight Princess come in a variety of colors, but not to differentiate strength. Rather, if you fill the remains of one in a bottle, it's color determines the effect of using it. If two different-colored Chus combine, the result is the default color, which was pretty worthless.
 * Four Swords Adventures and The Minish Cap feature Fire and Ice Wizzrobes alongside the standard kind. Four Swords Adventures also includes Force Gem-sucking Wizzrobes.
 * Legend of Mana notably had Underground Crabs in the very first dungeon.
 * Okami has the same set of tactics with occasional additional attacks for the successive areas of enemies. Difficulty is achieved late in the optional extras with nigh-endless waves of enemies.
 * Games based on Bionicle, since the toys are pretty much like this. "You are attacked by an Air Burnak." "You are attacked by a Stone Burnak." "You are attacked by an Ice Burnak."
 * Cave Story has a nice variety of enemy types, but recolors the critters (those beanbag-looking hopping things) and bats in several different caves.
 * While the main-series Kingdom Hearts games largely avoid this by simply scaling the strength of enemies found in later worlds, 358/2 Days plays it straight, with up to 3 different versions of many mooks where the only difference is size, a design choice that may have been mandated by limited space for the game data.
 * Resident Evil series has several: the Brain Sucker in 3 is an upgraded skin-swap of the Drain Deimos, the Sweeper in Code Veronica is a poisonous version of the Hunter, RE 2 has Super Lickers, the Iron Maiden in RE 4 is a more demonic version of the Regenerator, etc.
 * In Jabless Adventure, there are regular forest-dwelling bears, a SCUBA-diving bear, and a volcano-dwelling bear with a flamethrower. There's also the slimes, which get Palette Swapped and appear in darn near every area of the game.

Beat Em Ups

 * Double Dragon did this. While it certainly wasn't unusual or unexpected for a game of the arcade era, the fact that all of your opponents were human meant that different coloured characters got rather stupid toward the end. Whilst a man with brown or pink skin made sense, the same character with better fighting skills and blue, grey or green skin later in the game was cause for raised eyebrows.

Fighting Games

 * The queen of palette-swap fighting is arguably Dissidia Final Fantasy. Every enemy in the game is just a crystallized palette swap of the 22 characters you can use in the game, and all the bosses are just those same characters, only normal. And it has a single-player mode that can last up to 40 hours or more if you have to beat every bonus chapter. So you better hunker down and get ready to fight Tidus about 500 times or more. The only enemy that is at all different is the Final Boss, Chaos.

First-Person Shooter

 * Metroid Prime 2 recycled a lot of enemies from Prime 1 with new models. Some were barely changed (like the recoloured Triclops) while others were given a complete overhaul, the Beetle becoming the much smaller Splinter, the Elite Pirate the Ingsmasher, Baby Sheegoths becoming Grenchlers, Chozo Ghosts becoming Pirate Commandos, etc. There's also a few examples in the games themselves, like the normal / ice / plate Parasites in Prime and the light / dark creatures in Echoes.
 * The Ingsmashers simply reused the elite pirate combat codes from Prime 1 with only a small tweak being the shield thingy.
 * Speaking of light and dark, several enemies are barely fought in their normal form before the Ing show up to possess them
 * Done to a much less noticable extend in Prime 3, though the Phaz-Ing are rather noticable for being the exact same enemy as in Prime 2, but of different origin, so them being named after the Ing from the previous game makes absolutely no sense.
 * Amusingly, Prime 3 also did this with energy pickups. First, you have the classic energy balls, then phazon after acquiring the new suit, and finally anti-phazon in the last section of the game.
 * FPS games regularly do this with at least one of the more basic enemies (but tougher opponents sometimes get the same treatment). In the older era, this was done by changing the colouring of otherwise identical sprites, in 3D games it takes the somewhat more advanced and differentiating form of using different skins for the same model (or even different models for the same enemy). Common expressions of this includes;
 * Different weaponry and/or levels of toughness of the opponents (e.g. the processed humans of Quake II, the Cabal followers of Blood, Barons of Hell and Hellknights in Doom and Doom II).
 * Somewhat different abilities between the enemy types (e.g. the semi-invisibility of Spectres in the Doom series, the personal teleporters of Alien captains in Duke Nukem 3D)
 * Just plain diversity, especially common in regards to enemies meant to be more or less regular human beings. This in order to avoid the effect of feeling that the enemies faced are the same individual cloned countless times, usually to the effect of creating the impression that such cloning rather took place on three to five different individuals instead.
 * In Turok 2, Blind Ones, Fireborns, and Troopers are skin swaps of Sentinels, Endtrails, and Mantid Soldiers, respectively. The former two are literal underground mooks.
 * In the first two Halo games, the Elites got different-colored armor based on their military rank (Authority Equals Asskicking by the way). The higher classes, such as Honor Guards, and Councillors, as well as Generals and Field Marshals in Halo: Reach, also have more ornate armor. In Halo 3, the Brutes got a similar treatment, with each higher rank having more elaborate armor, and sub-ranks (Major, Minor, Ultra) being represented by palette swaps. The highest class, Brute Chieftains, have red or gold-accented black armor and warbonnet-like helmets.
 * The later levels of Pathways into Darkness feature Ghasts (aka Earthquake Zombies), Venomous Skitters (which as their name implies, inflict poison status), and Greater Nightmares(who are armored and shoot homing projectiles).
 * In Borderlands, when you're done with your first playthrough and start on a second one, the enemies get more health and different names, but their models don't change. Played straight in the first exapansion and the final expansion, which featured zombified and "-trap'd" enemies. The zombies had noticably different AI, but the claptrap-ised enemies just had different skins and dialogue.

Hack and Slash

 * Diablo I and II were full of this. Every single enemy in the games, apart from quest specific bosses, came in various levels of strength denoted by colour and had otherwise identical sprites as others of its type. It's mentioned in the first game manual that this is because the Prime Evils, the leaders of the demons, would alter their servants forms to better deal with whatever threat they were facing at the time.
 * Diablo III will probably be the same. Trailers indicate that it will also allow monster subtypes to vary in size.

Maze Games

 * It all started with Pac-Man, where the color coding of ghosts let the designers get away with only having one enemy type -- the colors indicated different AI strategies in how they pursued the heroic circle.
 * Many early arcade games did this, due to the hardware limitations of the day. Some examples include Berzerk, Missile Command, and Pengo.

Metroidvania

 * Super Metroid had half a dozen different colours of Space Pirates, of increasing power. From the wimpy grey Pirates in Old Tourian to the nasty red variant in Maridia that required the plasma beam to harm. There were also a pair of gold Pirates that served as sub-bosses before Ridley's lair.
 * Monster Tale applies it not only to the enemies but also to one of the heroes; Ellie's partner Chomp has three basic body types (Child, Teenager, and Adult), and all of Chomp's various forms are variations of those - one may be the basic form plus wings, another plus a tail, with spikes, with just one eye, etc.

MMORPGs

 * Guild Wars Eye of the North has plenty of enemies recycled from the three previous campaigns, but the most egregious example is re-using a species of monsters called "Mandragors". These insect/plant hybrids are found in the deserts of Nightfall, burrowing under the sand. In Eye of the North, identical monsters with the same name live in cold climate and burrow under snow, without as much as a Lampshade Hanging to explain it.
 * See also: the frogmen (though this is lampshaded by the fact that each color appears to designate a different tribe. This doesn't stop them from being modified versions of the Heket from Nightfall, though)
 * At the same time, Guild Wars will often subtly alter the mesh of different "species" of the same sort of enemy (the Tengu, the minotaurs, the Nightfall insects, and so on)
 * Specifically, ArenaNet will keep the skeleton of a mob intact to make use of its animations, but rework the attached mesh. The most obvious example of this is the Margonites. Several use basic class skeletons, but others used include the Damned Cleric, Mursaat, Seer, and even the Undead Lich, an end-game boss.
 * World of Warcraft changes the colour and increases the size of a monster to indicate that it is a higher level. Nearly every zone has some version of a wolf or boar to kill.
 * As humanoids go, nearly every zone has some version of a gnoll or murloc. They are just everywhere!
 * Played extra-straight with the monster (and quest) Terokkarantula. Tougher than the smaller spiders nearby, as would be expected by it's named nature and elite status, the player who hasn't been there before is probably STILL not expecting a spider that's larger than a good-sized HOUSE.
 * Somewhat averted in expansions as the developers go through a good deal of work to create a few "unique" creatures for each expansion (especially the alien planet Outland). Still, you're unlikely to hit a zone that doesn't have at least two or three models you've seen before.
 * An extra bit -- some of the more recognizably human of the undead monsters you fight use the same model types available for Undead characters (Justified as they share a common origin -- reanimated by the Scourge).
 * It is found already with the creeps in Warcraft III
 * Lord of the Rings Online -- similarly to World of Warcraft above -- re-skins meshes all the time. I have lost count of the different types of boars, worms, and wargs.
 * They have even hung a lampshade on the practice with a quest in Evendim, in which you are sent out for your umpteenth "kill me some boars" quest.
 * Which was further Lampshade Hanged in a later introduced dungeon in Evendim,
 * Ever Quest 1 used this extensively. It may have been possible to fight a "variety" of Skeletons -- sharing one model and possibly one texture (with Palette Swaps) -- all the way from level 1 to max level.
 * Everquest 2 has some sort of skeleton or zombie in almost every zone.
 * Perhaps parodied with Kingdom of Loathing with the perpendicular bat. Its description when you fight it is "This bat is perpendicular to the ground! That makes it totally different from a regular bat!" Definitely parodied with the completely different spider, which is nothing of the sort.
 * Adventure Quest's many different Zards definitely qualify.
 * Prior to the first update in RF Online there were a fair number of reskinned creatures, although the story behind them made more sense. When the new "Episode" addons were introduced, many of the creatures were recolored and resized for the newer areas. In fact even the players became this, as equipment above level 50 would be a reskin of an earlier piece of equipment. The newest update migated this somewhat with Elfland, where the reskinned enemies were few and far between, and a lot of new models were made for it. Too bad you wont get a chance to enjoy it.
 * Mabinogi is a particularly egregious user of this trope. There are a very limited number of enemy types; and they tend to get recycled constantly. The most blatant example are mongooses in Iria. They exist in nearly every part of the Maiz Prairie region, and are indistinguishable except by tail colour (even their names reflect this), with each colour indicating a different difficulty level.
 * Ragnarok Online mostly averts this, save for the Poring line of monsters, which difficulty ranges from very easy to event bosses capable of taking out GMs.

Platformers

 * Likewise, in Super Mario Bros., red-shelled Koopas were implied to be "more powerful", at least in that they had enough sense to not stroll off of cliffs like their green counterparts.
 * This led to the Green Koopas marching in straight lines unless they came upon some sort of block or another enemy creature (like a Goomba), which would make them turn around. (They also tended to turn around if they walked into you, which was easiest to see when the action froze as Mario fell off the screen.) Red Koopas behaved the same way, except that they also turned around when they came upon a cliff (instead of just walking off the edge like the green ones.)
 * There was a much greater difference between the Green and Red Paratroopas. Green ones tended to hop along in a straight line (leading to major headaches as you were forced to decide whether to try to dash beneath them or hop over them, and more often than not wound up in the wrong place at the wrong time); red ones just flew back and forth, "patrolling" a specific area without changing elevation. Sometimes the red ones instead flew up and down without any horizontal movement, and occasionally the green ones did that too. In any event, once you stomped on a Paratroopa and knocked its wings off, it would revert to the AI of its ground-bound counterpart (not that you'd notice if said former Paratroopa fell into a Bottomless Pit).
 * In Super Mario Bros 2, Shy Guys came in pink and red, with pink being the marginally smarter. However, Snifits came in a rainbow of colors, each with different behavior.
 * And yet there was only ever one red Snifit.
 * The Paper Mario games are prone to this in the later areas. Although each chapter tends to have its own set of themed enemies, a few will return as recolours.
 * Super Mario World has four colors of Koopas. Yellow drops from ledges like green, moves faster, drops a coin when taken out of its shell, and can jump into a shell to make it into an "invincible" flashing shell (or "disco shell"). Blue doesn't fall from ledges, and recovers much faster than the others after getting knocked out of their shells (they're also much thicker, implying they're stronger) and usually kick the shell away instead of reentering it.
 * It also affects the powers Yoshi gets from them: Green does nothing, red gives him a one-time flame attack, yellow makes him damage nearby enemies upon touching the ground, and blue lets him fly. Flashing shells give all powers at once.
 * For that matter, Yoshi himself: A green Yoshi eating a shell only gets the shell's power, but a non-green Yoshi also gets the power from his own color (so a blue Yoshi can fly with any shell).
 * Wario World does this a lot. There's a few unique enemies, but generally there's about four or five standard enemy types, and each world just changes the theme of them. You've got Magons, which then get reused as Skeletal Magons, Clowns, Snowmen, Wolves, Puppet Magons and Mummy Magons. You've got Cractyls which come as Bone Cractyls, Pigeons, Snow Bombers, Hawks, Masked Crows and Mummy Hawks. And the same for another four or so types of enemies.
 * Played straight in Wonder Boy III: The Dragon's Trap. Red foes are weak, green are stronger, and blue are the strongest, often with the blue variants being given surprisingly powerful attacks after the player had gotten used to fighting the weaker variants.
 * In Keith Courage in Alpha Zones, the Final Boss, the Titan Warrior, is a gold Palette Swap of Mr. Roboto, the boss of Area 4.
 * Several of the bosses in Wonder Boy in Monster Land do this, such as the Red Knight/Blue Knight/Silver Knight, the Grim Reaper / God of Poverty, and the Giant Kong/Snow Kong.
 * In Purple, basic mooks like slimes, bats and cannons get Palette Swapped at least three times, each with a slightly different behaviour.
 * In the first Donkey Kong Country game, Krusha came in two varieties. The first kind was blue with green camo and was only beatable by either of Donkey Kong's main attacks or a barrel (Diddy Kong's attacks were laughed off). The second kind only appeared once in the SNES version, in the very last level before King K. Rool. This version was grey with purple camo. The only thing that could beat him was a barrel, making him the strongest of the Kremlings.
 * Descent: The Super Hulk or Super Mech is a red version of the Medium Hulk that is much tougher and armed with homing missiles. The Fusion Hulk is a scaled down version of the first boss armed with a Fusion Cannon. In the second game, the Spawn is a green version of the Red Hornet, and the Tiger or Red Fatty Jr. uses the same model as the first boss, although it is smaller and has completely different weapons.
 * Bug!! You fight snail enemies in Insectia Scene 3, each of which were very slow and took three hits to die. And then when you get to Splot, you see them again. Except that they take nine hits, and move twice as fast. And when they see Bug, they take out freaking MACHINE GUNS from their shells and fire at him!

Real-Time Strategy

 * Nigh-on every non-boss enemy in Super Robot Wars OG Saga: Endless Frontier, presumably to make room for more boob jokes.

Turn-based Strategy

 * In all of Nippon Ichi games higher variations of Player Mooks classes are recolors of their basic sprite.
 * Shining Force uses this extensively in all of its games.

Roguelike

 * Roguelike games employ this device to a fare-thee-well, since all of the monsters are represented by ASCII symbols, color coding is often the only easy way to tell them apart. Of course, sometimes two monsters have to share the same letter and color. Which leads many players to use alternate graphical "tile sets" which offer more information. Whether or not you should do this is one of the major fault-lines in Nethack fan circles. Of course, this also led to isometric sprite based clones (Vulture) using mini-map and shortcuts in the original Nethack style.
 * It's interesting that this trope still appears in roguelikes not just in that the monsters look the same but in that there are different variations of the same monster, even though in those there is NO work required in generating sprites for new monsters, so the imagination is the only limit. Given that Angband has close to 1000 unique monster types, the reason for this happening in such a game is probably more that the designers started running out of ideas rather than not being able to animate distinct monsters.
 * Dwarf Fortress inherits this approach, including the tileset option. For example, color is usually the only way to differentiate between rocks of different ores (which can be very important when you need to smelt metals) without checking what's on the specific tile.
 * In Nethack, this can also lead to Yet Another Stupid Death, in ways both obvious and surprising. Not only might the player not distinguish between a dwarf lord and a mind flayer, in some contexts the game itself doesn't distinguish between them. Ooh a blessed scroll of genocide! You'd better cap the mind flayers, having to remap levels is a bitch. What's that? You were playing as a dwarf? Congratulations: you have succumbed to death by palette swap. (Blessed scrolls genocide a class of monsters, in this case h, Humanoid)
 * The sprite based Roguelike, Dungeons of Dredmor, has an absolute ton of these sorts of monsters. Most have different effects - Diggles are just annoying, but Sickly Diggles debuff you and Diggle Commandos are invisible.

Role-Playing Games
""There's also supposed to be a camouflage-coloured ninja, but no one has ever seen him"."
 * Morrowind had a considerable lack of diversity amongst its native fauna, resorting heavily to underground monkeyism to create a wider range of enemies. This was somewhat justifiable in the sense that most of the game took place on a single island, and travelling northwest to the island of Solsthheim introduced you to a set of entirely new creatures.
 * Super Mario RPG has this with a LOT of enemy types. Sometimes in quick succession.
 * In the Dragon Quest/Warrior series, one of the first common enemies you encounter is the blue slime. Then, you meet the slightly stronger red slime. And as the series progressed, the Heal Slime. Then the Metal Slime. Then the King Slime. Then the Metal King Slime. Then the Mons game showed up, and you got Treeslime, and Wingslime, and Halo Slime, and... All the way up to the exceptionally powerful, Akira Toriyama-inspired (and designed!) Nigh Invulnerable Platinum King Jewel. It also featured color-coded dragons.
 * Dragon Quest Monsters Joker 2 takes this particularly Up to Eleven, where the strongest slimes include a Henshin Hero slime, a Kill Sat slime, and a Humongous Mecha slime!
 * The majority of monsters in the series have at least one recolor, including regular bosses. In fact, the secret boss of Dragon Quest 6, arguably the single most glorified, powerful antagonist in the franchise, is a palette swap of an earlier boss. It's easier to count the few enemies with unique sprites.
 * Dragon Quest Heroes Rocket Slime. Each of the 100 different members of the Monster Town is a different type of slime.
 * Final Fantasy uses this in most incarnations, especially with the Elemental Rock-Paper-Scissors aspect: the blue monster casts water spells and is weak against thunder, the white monster casts ice spells and is weak against fire, etc. Final Fantasy X made some extra use of this, as a side quest rewarded players for capturing entire "species" of monsters. It was especially common in the earlier, sprite-based games due to Palette Swaps.
 * Final Fantasy XI has tons of instances of monsters that look exactly the same, only stronger and with a different name, including several Notorious Monsters.
 * And when monsters of the same species don't look exactly the same, they are palette swaps. In some cases this is justified. For example, rabbit type enemies have different fur color in different climates. It gets a little harder to justify with the Wings of the Goddess expansion, where forest tigers from 20 years ago are neon orange for no apparent reason.
 * Final Fantasy XII manages to subvert the spirit of this trope without subverting the letter of it, by making slight differences in the meshes of any given group of monsters (i.e. some toads have claws, others have webbed feet).
 * More prominent example: the Hellhound has a large horn that the Desert Wolf does not.
 * Final Fantasy XII also justified it to some extent, as many of the monsters who share a given sprite are in fact related to one another, as the Bestiary implies.
 * Final Fantasy XII is a good example of how to do palette swap enemies, with different species of monster varying by environment: their primary diet, the climate, and some being mutations caused by Mist.
 * Crisis Core: Final Fantasy VII took this to ridiculous extremes. If a monster got a special white coloration with feathers, & a pattern of a certain character's face, it became a 'copy' of said character. Despite essentially being the same monster, it was implied to be much more powerful as a result.
 * Worse yet, after a certain point, they didn't even bother to change the enemy colors. This left you with about 200 missions of fighting the same, boring avatars.
 * Both Final Fantasy VIII and Final Fantasy IX avert this trope, where (almost) every monster type in the game has a unique mesh, animation, and sound effect. The only exceptions (for VIII, anyway) are for human and humanoid enemies.
 * IX has a few palette swaps; the ten Fairy Battles, and the Crystal versions of the Four Fiends.
 * Gameboy games had the lack of memory needed to justify Underground Monkeys, but, being monochrome, had no way of switching palettes. Generally, this led to enemies either never improving or simply gaining more hit points, though turn-based RPGs (Such as the SaGa/FinalFantasyLegend series) were able to circumvent this by... giving the sprites new names. (Say, isn't that Master Dragon the exact same size as the Baby Dragon from the start of the game?)
 * Interestingly, this hardware limitation led to an inversion in Metroid 2. In the original, getting Samus's Varia armor made the sprite change color, which wasn't possible on the Gameboy. To compensate, gaining the upgrade gave the Varia suit the huge shoulders that are now the character's trademark look.
 * Metroid: Zero Mission, which is a remake of Metroid 1, lacks the round shoulders on the Varia Suit. However, near the end of the game, Samus's Power Suit is destroyed, and she obtains a new one. The new one has the large shoulders. The end of Zero Mission takes place in the immediate aftermath of the ending of Metroid 1, and as such explains how Samus came to possess the Metroid 2-style Varia suit.
 * But not how she came to lose it again...
 * In the Fallout games, a common practice was to have different individuals represented by a sprite of the same person (usually the male and female sprite used for the Player Character, no less) stuck in a different suit of armour or clothing. The second game in the series contained a couple of self-conscious Lampshade Hanging jokes on this theme, including the henchman of a crime boss confiding that he suspects there must have been a big cloning accident at some point in the past, and an Easter Egg location in which a pair of sprites originally intended to be player characters but retooled to only fill NPC duties lament over their fate.
 * Fallout 3 is a more modern 3D game and as such gives every human character different appearances. And while all Feral Ghouls look the same, the different species of Ghoul are easily identifiable. Ferals are the standard, Reavers get a different face and abilities and Glowing Ones... well, glow. Normal Super Mutants, Overlords and Behemoths are very easy to tell apart and are fought with different strategies; unfortunately the Brutes and Masters only have slight armor and HP varieties from the standard ones. Other monsters in the game usually only have one type. Then comes the Point Lookout expansion, which adds swamp versions of Ghouls and Mirelurks... and they are definitely just Palette Swaps with slightly different effects on their abilities.
 * In Brave Story: New Traveler, the exact same enemy can come in multiple different colors, so the difference between genuinely different enemies is at least slightly greater, with a few exceptions. This editor isn't quite sure how to label this.
 * Multi-Colored Monkeys?
 * This was part of the game's world design. Monsters were designed to be "organic" in that one given monster species would have biodiversity. The player could encounter three mobs in the same battle, and each would have slightly different stats. In general, colour had less to do with power than size, with larger mobs being significantly stronger.
 * Persona 3 is another good example of this trope--practically every enemy inside Tartarus, the game's sole real dungeon, uses one of a select number of sprites, and most sprite-sharers are vulnerable to the same kinds of tactics (if not necessarily always sharing elemental weaknesses).
 * Not only that, but every boss not important to the story is simply a giant version of a normal enemy, a practice that would carry over to Persona 4.
 * Note that this is a Justified Trope, due to the nature of the Shadows.
 * Persona 2 also has a small handful of these, thanks to palette swaps and the occasional replacement part in monster sprites (several Chariot Arcana demons the most obvious of the latter, using the same giant brute body with different heads and colors).
 * The Monster Hunter series uses this repeatedly. A prime example is the Kut Ku, one of the easiest wyverns in the game, which appears later on as the Blue Kut Ku, a stronger (and blue) version identical in every other way. Not only does the game do this with the enemies, but the armour then made from the enemies looks exactly the same apart from a colour swap to fit with the wyverns' colour.
 * Some other examples of monster counterparts behave exactly the same but have very different appearances. For example, the Aptonoth looks like an amalgamation of different species of dinosaurs, while the Tundra-inhabiting Popo looks like a very short, trunk-less woolly mammoth. Both species behave pretty much identically, and they both fill the role of the harmless herbivore that gets eaten by everything else.
 * Grandia II starts doing this about halfway through the game.
 * Pokémon notably does not perform "PaletteSwaps" of its monsters (aside from the rare "shiny" Pokémon, which are explicitly the exact same species as the non-Shiny versions, only with some sparkly-ness). The closest thing to recycled enemies might be evolved forms of previously encountered Pokémon, or simply the same Pokémon but at higher levels. This lack of palette-swapping monsters makes logical sense when you consider that the whole premise of the game is built on having a wide selection of Pokémon to customize your team with. There are, however, many Pokémon that fall under the "similar but with different element" category, such as the Fire, Ice, Lightning trio of Legendary birds from the first generation -- Articuno, Zapdos, and Moltres.
 * Played completely straight with some of the Trainers - While there are no palette swaps, and the in-battle sprites of the Trainer types are all unique, often several types share the same overworld sprite, so that in Pokémon Diamond Pearl and Platinum, for example, Ace Trainers and Rangers look the same until you fight them (and the sprite is clearly that of the Ace Trainers). The most egregious example is perhaps the Rich Boys, Psychics, and PIs/Gamblers. PIs/Gamblers wear a fedora and a trenchcoat in battle, while Psychics wear a purple jumpsuit with greenish hair; the overworld sprite used for all three clearly has the Rich Boy's dark purple hair and white suit.
 * Although the reasoning behind PIs having Rich Boy's look could be the fact that they're supposed to be incognito. Psychics and Gamblers, however, have no excuse.
 * Also played straight with the cry sounds. There were only about 30 cry sounds in the original game, and while some were sped up or slowed down, some cries, even by unrelated Pokémon, were identical. Charizard and Rhyhorn, Ditto and Poliwag... Caterpie and Goldeen technically have different cries, but you'd have to listen to them in succession to hear it.
 * Interestingly, this was played straight with Shinies in Pokémon Gold Silver and Crystal: unlike in later games, which have a "shiny flag" on the Mons, Pokémon with specific base stat totals were Shiny, which resulted in Shiny Pokémon having somewhat higher base stats.
 * Played straight once more with one of the legendary trios for Pokémon Black and White. Tornadus, Thundurus, and Landorus all look nearly identical.
 * Don't forget the elemental monkeys Pansear, Panpour, and Pansage plus their evolved forms, complete with identical cries to boot.
 * Also, Pidgey and Spearow. And Taillow. And Starly. And Pidove.
 * And also Pachirisu and Emolga.
 * Pikachu and Raichu, Pichu, Plusle and Minun...
 * Taken to a more extreme level by the Wizardry games, particularly VI and VII, wherein enemies were given graphics by type-all slimes use the same graphics, as do all demons, all bugs, etc, including non-hostile NPCs and bosses. Further complicating matters is that unless a party member has a high mythology skill, all you'll see attacking you is generic "birds" or "crawling wastes". Experienced players can usually determine what particular monster is attacking them by the area they're in or the attacks the monster uses. Occasionally leads to party kills when the player mistakes a very nasty enemy for an easy one.
 * Chrono Trigger includes the "Debugger" and "Debuggest" robot-bug enemies; "Rolies", "Polies", and "Rolypolies"; "Cave Apes" and "Goons"; and "Mutants" and "Metal Mutes", among others.
 * Don't you mean Roundil-*is shot*
 * It also features literal Underground Monkeys. With wings.
 * Golden Sun has this all over the place, although there are certain occasions where an enemy will be slightly powered up without changing the name/color.
 * There are even some unused variants of certain enemies hidden in the game's coding, complete with differing Palette Swaps and names.
 * The later sprite-based Might and Magic games, especially the seventh incarnation, played this trope hilariously straight. How do you tell the difference between a minotaur and a minotaur lord? The nastier version is almost identical - it's just a bit bigger. And bright purple.
 * Ditto on Elona
 * Albion does this a little differently. The enemies are different on each continent, but come in a small variety. Stronger versions of certain creatures accompany larger packs. They don't even bother with creative names (Animal3)
 * The World Ends With You has four or five varieties of every monster type in the game. Including bright pink elephants. At least they have slightly differing attack patterns and (sometimes) vulnerabilities.
 * When you're drowning in a sea of work with not enough time,...why pour your soul into assets that get used all of... what, once? Really. Have some compassion.
 * MOTHER, although otherwise unrelated to this trope, had a tribe of Cloudcuckoolander monkeys living underground in a desert.
 * Actually, Mother plays this trope quite often. For example, the Lone Wolf, Silver Wolf, and Wolf are all the same sprite with different colors, and the Stray Dog is a wolf sprite colored brown with a chain around its neck.
 * The entire trilogy does this, although Earthbound and Mother3 give the palette swaps goofy names. For instance, you have the 'Manly Fish' and his stronger swap, the 'Manly Fish's Brother'.
 * The Swedish parody RPG Playelf has this with ninjas - there are red ninjas, blue ninjas, black ninjas, white ninjas, etc - as well as "hurry up-ninjas" which appears when the players are dithering. But the most awesome ninja...


 * Present throught out the Tales (series). Monsters that are purely palette swaps are most common in the games that utilize sprite based graphics, while the 3D games usually change their model a little, as well.
 * Boktai has this in all its incarnations, though sometimes coloration is used as a hint to its elemental affinity. This is more egregious in Lunar Knights, where many enemies are colored solely by affinity - namely, the Ghouls, Vorns, Slimes, Hounds, and Chloroformin' come in different colors on this alone. The Slimes, strangely enough, are the only ones in this group that come in Sol flavor.
 * Ultima V contains literal monkeys found only underground -- the Mongbats -- but they resemble nothing else in the game.
 * Ultima III has multiple enemy types with the same colours where the only difference is the name - however, that's literally the only difference. No change in stats, health, damage dealth, weaknesses... Just Orcs, Goblins and Trolls, all exactly the same.
 * This isn't often used in the Shining Force games, but when it is, it is jarring. the original Shining Force, for example, had th regular Bats, and their aquatic cousins, Sea Bats.
 * Hyperdimension Neptunia has this in spades, especially considering some of the monsters are from other games.

Multiple

 * Digimon as a whole loves this. The anime itself has recolors who are merely a different attribute (such as say, Black Rapidmon, who is a Virus-type counterpart to Rapidmon), different element (such as Yukidarumon and Tsuchidarumon, snow and ground respectively), or just a recolor for the sake of being a recolor.
 * The Digimon games add to this by not only having the original recolors included, but several entirely recolored evolution lines, Rookie to Mega, in Vaccine, Data and Virus flavors.
 * Taken to an absurd extreme with Soulmon, who is a Bakemon with a wizard's hat. That's the ONLY difference.

Tabletop Games

 * Color-coded dragons predate most video games, as they appeared in the Tabletop Games Dungeons and Dragons, which was first published in 1974. Evil ("Chromatic") dragons have scales of a particular solid color reflecting their place in the Elemental Rock-Paper-Scissors spectrum, and good ("Metallic") dragons have scales of precious metal. Interestingly, though, these aren't "palette swaps"; as it is possible to readily identify different species of dragons in greyscale artwork (for example, white dragons have a peculiar vertical crest on their head, while silver dragons have backward-pointing horns and a ribbed frill along their necks).
 * On one occasion, the color-coding is used as the basis of a truly heartbreaking Monster Is a Mommy story, when a noble silver dragon is born with albinism, and is hunted down and killed by an adventurer who thinks it's a white dragon.
 * One adventure featured a similar story with an albino red dragon, causing the party to prepare to fight it in the least effective way possible.
 * This was parodied in the webcomic Order of the Stick: in one comic, a paladin discovers the titular party has killed a dragon. She then accuses them of possibly killing a creature of benevolence and wisdom, and asks why they thought it deserved death, to which Roy Greenhilt replies, "Erm... its scales weren't shiny?" which placates the paladin. Elan then breaks the Fourth Wall by winking at the reader and saying, "Dragons - now Colour-Coded for Your Convenience!"
 * Ironically, the comic does this itself with goblins/hobgoblins/ghouls.
 * Rothé are bovines resembling musk oxen. That have magical variants too: underground "deep rothé" is about 4' at the shoulder, still charging in herds, with infravision and communicating via dancing lights and "ghost rothé" is bison-sized, white and capable of stampeding under magical silence.
 * The Elves of D&D come in high, wood, sea, grey, wild and several other varieties.
 * The third edition of Dungeons and Dragons features templates, giving uncreative GMs the opportunity to color-code any monster into a water monster, a fire monster, slime monster, etc.
 * Although one 3rd edition Dragon article about creating monsters included "But this one's blue!" in a list of how not to do it.
 * Fourth Edition includes at least one extra variety of every monster in its Monster Manual entry. Many of these fall into Underground Monkey status, being simply higher level versions from a different environment-normally, a different plane. Notably, the Feygrove Choker is a reverse Underground Monkey, being a creature from thick forests in the Feywild, while the base creature lurks in the Underdark.
 * While discouraged due to the WYSIWYG rule of the game, Warhammer 40000 still has shades of this. Space Marines have more rules than the rest of the other playable factions combined, and the only way to tell them apart is by their armor and what kind of bling they have (Robed and Green, it's probably Dark Angels. Spikey and/or evil looking, probably Chaos. Red and Blood drops, Blood Angels. Knightly helmets and book emblems, Grey Knights. Swords and seals, Black Templars, etc...). Even within a single army, the difference between an elite squad of veterans armed with modified boltguns and a simple tactical squad is sometimes literally a differently painted shoulderpad. Averted with the other races, where each type of trooper generally gets their own model.
 * There's now specific models for veteran Space Marines, with custom boltguns that look a bit different and shoulder pads that have embossed icons for non-codex chapters. Of course, these models are more expensive, so some players stick with the old palette swap method.

Toys

 * Other toys use a similar system, often called redecos (when identical molds are used but the color of plastic is altered) or retools (when most parts stay basically the same but are altered to include, for example, new accessories; this can also include a redeco). For example, in the most recent series of Transformers, Stormcloud is a redeco of Powerglide, while Sideswipe is a retool of Sunstreaker.
 * This even leads to recolors in characters in the cartoon--for example, Thundercracker and Skywarp were repaints of Starscream. This became very confusing when someone accidentally colored two Starscreams.
 * The most annoying use of this in recent series has been making Galvatron a redeco of Megatron.
 * For most of its run, Bionicle sets were just recolors of each other with slight differences in assembly and parts. Sometimes, the only difference would be their masks and their tools/weapons. Then, the Mahri Nui saga came along in 2007, and the Barraki were released, each looking very different from each other. Since then, the sets have been largely Averted this trope.
 * Played with in the larger sets. While each large set was in of itself different from other large sets, each early large set could produce two near-identical creatures. Justified in that back then Bionicle toys were more akin to Rock'em Sock'em robots, and the kids were expected to play against eachother so the toys had to be identical to make it fair. Newer large sets averts this since they lost the Playability of the older sets in lieu of posability.

Web Comics

 * Gets parodied in the Sluggy Freelance "Years of Yarncraft" (spoofing World of Warcraft, of course) here, here and here.
 * As mentioned in the trope description, the Trope Namer is RPG World, and was originally a Lampshade Hanging by showing a number of "Underground (animal not usually found in caves)" enemies in succession.

Real Life

 * Truth in Television: Members of the same biological genus are usually similar enough that the main differences are color and location. Things like size, basic body shape, and diet are all almost identical.