Gotcha Monster

The Wolf-In-Sheep's-Clothing, one of the more bizarre awesome D&D Gotcha Monsters, in action.

Gotcha Monster is a slang term used in /tg/ circles to refer to any of the wide array of monsters whose hunting strategy revolves around disguising themselves or lurking in seemingly innocuous places and then trying to kill adventurers the moment that they let their guard down even the slightest. The term is most associated with Advanced Dungeons & Dragons and Old School Roleplaying, which gave rise to some of the most infamous species of Gotcha Monsters in existence, but the basic idea can be found pretty much throughout gaming circles. They are, at base, biological traps.

There is a case to be made for Gotcha Monsters: the camouflaged-ambush type is a type that, in fact, exists in our real world. We'll make that case more fully in its own section; below all the (many, many, many) mostly-fantasy examples. One serious case against: they're just traps. Once you've introduced one example, like the Roper, the party knows that prototype exists, and if that party meets another of that type it's just ... boring, you know.

A Game Master who relies on using Gotcha Monsters to excess is known as a Killer Game Master. Or as a dick. Or else as a... designer of a 1970s tournament series, where most of them started.

Eric Holmes and Tom Moldvay hated them and didn't permit (for a start) the Water Weird or the Roper up to Expert Set; Frank Mentzer more than agreed and would exclude them from Companion Set as well. Despite including a lot of other 1970s shit in there like the thoul and that Tarantella Spider.

Some also argue that monsters which do not directly attack players, but damage their combat abilities in some way, such as Rust Monsters and Disenchanters, also count as Gotcha Monsters.

Not to be confused with Gacha Monsters.

D&D Gotcha Monsters

Aside from slimes, golems, therianthropes, carnivorous plants, and shadows, which can easily be portrayed in this way, D&D has a long list of Gotcha Monsters.

Aballin

A slime-like creature that resembles a mass of animate water, which it pretends to be before drowning and digesting anything that attempts to drink from it.

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Adherer

A monstrous humanoid which looks like a mummy, but which is actually a living being covered in fibrous skin-strands that secrete a gluey resin. They use these to catch an adventurer's weapon and rip it out of his grasp, whereupon they can beat him to death. First appeared in Fiend Factory as the "Gluey".

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  A Pathfinder adherer fighting Carmen Sandiegorc.

Alkilith

A demonic ooze that has multiple ways to be a Gotcha Monster, from the subtle way of corrupting anyone that touches it to the instantly deadly way of opening a portal to the Abyss if it manages to surround a doorway or window frame with expected results. It might even pull you into that hellscape if you're not paying attention to if that doorway is actually surrounded by moss or not.

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Animated Object

Could be a table, a chair, or just about anything in the room waiting to surprise you.

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Animator

An invisible spirit from Ravenloft that possesses objects and has spellcasting abilities. Comes in three types: Minor, Common and Greater. The more powerful it is, the bigger the object it can possess.

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Assassin Imp

Looks like a normal imp and can be summoned as a familiar. It is obsessed with killing anyone it sees as a "threat" to its master, which invariably includes its master's friends and family.

Bloodring (Ring-worm)

A blood-drinking (or magic-eating) parasitic worm that disguises itself by pretending to be an enchanted ring, as it can extend its own innate magic resistance to any creature it is touching. Appears as the Ring-worm in Monstrous Compendium: Forgotten Realms Appendix II, where it causes you to forget one spell the first day you wear it, two spells the second day, and so on.

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Bowler

Rocks Fall, Everyone Dies, but the rocks are sentient.

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Brain Mole

An ordinary mole that happens to feed on mental energy, resulting in it draining away memories and potentially leaving its victims as drooling vegetables if they get too close to its den.

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  ALL GLORY TO THE HYPNOMOLE

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Carbuncle

An armadillo-like creature with a valuable ruby on its forehead that it promises to give to the party. It secretly uses its psionic powers to attract monsters or goad the party members into fighting each other, then leaves when the combat starts. If you kill it, the ruby disintegrates.

Carrionette

A sapient, malicious marionette-type puppet that possesses independent motion and can swap bodies with its victims by stabbing them with a special needle.

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Carrion Stalker

It looks like a human ribcage filled with entrails, but the ribs are actually its legs, and the intestines are its slimy tentacles. It hides inside the mutilated bodies of its victims, waiting for someone else to get close.

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Chaos Imp

An annoying imp subspecies native to Limbo, which can "possess" inanimate matter and reshape it to their will, which they use to play potentially deadly pranks.

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Cloaker

A killer manta ray that disguises itself as a cloak to trick people into wearing it, which lets it eat them. From 3e onward they no longer disguise themselves as cloaks, and so aren't really gotcha anymore.

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Cushion Fungi

Carnivorous fungi that look like pillows and release soporific spores so people will sleep on them.

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Darkmantle

A stony squid with the ability to generate darkness that hangs from the ceilings of caves disguised as a stalactite and drops on people to smoother them.

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Death Linen

Killer pillow that smothers you in your sleep. Also comes in pajama and towel variants.

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Disenchanter

A creature resembling a blue camel with an elephant's trunk that sucks the magical energy out of magic items.

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• Laraken: A yellow ball with two tentacles. Same powers as the Disenchanter, but it can also suck spells out of mages and then use those spells itself.

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Dune Trapper

A giant desert dwelling creature that buries itself in the sand and disguises its mouth as an entire oasis. Native to Dark Sun.

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Dusanu

It looks like a Skeleton, but it actually is a Fungus that animates bones and not an undead and so doesn't have their weaknesses and it is also infectious.

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• Goop Ghoul: Basically the same as a dusanu, but the skeleton is being controlled by a slime. Has a paralytic touch.

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Ear Seeker

A wood-eating insect that often infests dungeons doors, and will bore into the ears of anyone who tries to listen at those doors, because they like to lay their eggs in the ear canals of humanoids so their larvae can feed on living brain tissue.

Executioner's Hood

Predecessor of the darkmantle. It jumps onto your head and strangles you to death.

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Explodestool

Do I really have to spell it out for you? It's a mushroom that explodes when you touch it. Appeared in Dragon #89

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Eye of the Deep

A relative of Beholders that likes to fool people at sea with illusions of things like mermaids.

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Gambado

A one-legged predatory monster that hides itself in a pit with just its head - covered in a seemingly abandoned skull - poking out. It then jumps out and tries to kill anyone who gets too close.

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Gargoyle

A vicious predatory creature that disguises itself as a statue in order to attack prey when their guard is down.

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Gas Spore

A floating puffball fungus that disguises itself as a Beholder; when burst by a spear or arrow, it explodes in a shower of lethally poisonous spores.

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Genius Loci

A living, malevolent piece of landscape.

Giant Black Squirrel

A 2ft-long, black-furred relative of the squirrel that inhabits "evil-dominated forests". Harmless, but likes to steal valuables from travelers.

Goldbug

A blood-sucking beetle that disguises itself as a gold coin to get close to its humanoid prey.

Heart Tick

An oversized tick that latches onto victims with its barbed legs so it can puncture their heart and siphon out the richest, most potent blood in their body.

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Hearth Fiend

Whenever a fire-based spell is cast in Ravenloft, there is a 1% chance that it will summon a hearth fiend, an invisible spirit that immediately possesses the nearest source of nonmagical fire. The flame then starts whispering to people nearby, attempting to charm them into doing evil.

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Heway

An intelligent snake which hunts by climbing into wells or ponds and then shedding its skin, which transmutes the water into a toxic fluid; it then eats anything killed by drinking the fouled water.

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Huptzeen

An animated object that can't move but can cast spells.

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Impersonator

A slime that can assume the form of anyone it has killed.

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• Oblex: Basically the same as the impersonator, but it also has all the memories of the person it's impersonating, and can disguise itself as multiple people at once as long as they are all connected by little cords of slime.

Lock Lurker

A vicious invertebrate that resembles a gold coin, until it extends its legs and the lethally poisonous, scorpion-like stinging tail it normally hides in the Ethereal Plane.

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Living Wall

A mass of undead flesh and bone melded together, which uses innate illusions to disguise itself as an ordinary stone wall until something living comes close, whereupon it tries to rip them apart and absorb them into its mass.

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Living Web (Duleep)

A slime-like entity that disguises itself as a mass of abandoned cobwebs, then engulfs and electrocutes anything that touches it so it can consume them.

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Lurker

A flattish monster, somewhere between a slime and a flying manta ray, that clings to the ceiling and then drops on people to smother them.

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• Trapper: A bigger version of the Lurker, which disguises itself as a dungeon or cavern floor and then rises up to crush and devour anyone who steps on it.

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• Miner: A forest-dwelling variant of the Trapper, which hides itself on forest trails and waits until victims step on its back, stabbing themselves on its numerous paralytic poison-carrying quills so it can then smother and devour them.

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Magebane

A bat-like creature that is invisible to everyone except the spellcaster it is currently fucking with. It follows the mage everywhere and drains the energy from any spells they cast, either lessening the spell's power or absorbing it completely.

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Millikan

Indistinguishable from a tree stump until it extends two tube-shaped orifices and becomes a living flamethrower, spraying oil out of one tube and setting it alight with a flame from the other. Appeared in Dragon #89.

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Mimic

A predatory slime-like creature which disguises itself as an inanimate object (most iconically a chest) to lure in humanoid victims. Larger mimics can disguise themselves as entire rooms or even buildings.

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• Marble Pudding: The evolutionary "missing link" between puddings and mimics. A slime that can harden its surface to disguise itself as a rock. Appeared in Dragon #251.

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Palimpsest

A piece of magic scroll parchment that came to life as a result of being recycled too many times. It absorbs absorbs anyone who touches it and can use their spells.

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Peltast

Looks like an item made of leather, such as clothing or a backpack, but when you put it on it starts sucking your blood. First appeared in Dragon #89.

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Piercer

A carnivorous gastropod which resembles a stalactite; it clings to cavern ceilings and then attempts to drop on anything that moves below, hoping to fatally impale them on its sharpened shell. In 5e they were retconned as the larval form of ropers.

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  Who would want a model of this thing?

Pseudo-Familiar

Whenever find familiar is cast in Ravenloft, you get one of these instead. They look like normal familiars, but they will magically drain hitpoints from their wizard and the other party members while they sleep. Gradually, they take over the minds of their wizards, who will then to try to kill the other party members.

Pseudo-Undead

Very obscure class of monsters from AD&D 1e that work just like undead, except they aren't really, so clerics can't turn them and any other undead-affecting spells or abilities simply don't work on them. We'd have allowed this for virus- or (maybe especially) fungus-affected still-living creatures like that dusanu; but noooo this template was allowed even for incorporeals, or for free-willed undead. It was just a terrible idea and thankfully, got shunted aside.

Quell

A ghostly undead with the ability to temporarily strip divine spellcasters of their abilities, taking away their advantages against undead.

Raggamoffyn

A set of clothes that take control of your body if you put them on.

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Roper

A tentacled monster that disguises itself as a rock outcropping, boulder or stalagmite until victims get within range.

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• Bi-nou: Pretty much identical to the roper in form and function, except it has two eyes and humanoid arms.

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Rot Grub

Voracious predatory maggots which infest mounds of dung and carrion, and which will leap to infest and devour living creatures that get too close.

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Rust Monster

A giant beetle-like creature that feeds on metal, dissolving arms and armor in pursuit of food.

Sand Vortex

Another Dark Sun creature that buries itself in the sand. When it senses creatures walking above, it creates a whirlpool of sand that pulls them into its mouth.

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Sheet Phantom

A malevolent undead which possesses a thick blanket and uses it as a physical body to try and grapple, trap and smother living beings.

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Shrieker

Mushrooms that scream really loudly and attract other monsters to you if you disturb them.

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Skullrider

A spider that can retract its legs and mandibles into its body, which happens to be the exact size and shape of a human skull. It also has the ability to hook itself up to the nervous system of a recently deceased creature and pilot it around like a goddamn mech.

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• Head hunter: Exactly the same as the skullrider except its skull is a fully fleshed human head. Native to Ravenloft.

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Spanner

An animated stone bridge that can talk and can throw you off or open a hole in itself to make you fall, so be polite.

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Stunjelly

A variant of the Gelatinous Cube which clings to a single section of stone wall and paralyzes anyone who touches it. Then it oozes over their body and eats them. First appeared in Fiend Factory as the "Living Wall" (not to be confused with the other Living Wall that appears in this list).

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Symbiotic Jelly

An ooze that partners with another monster and uses illusions to make the monster look like something less dangerous and lures in prey for the monster with illusions of things that they want such as treasure.

The Throat Leech

A small leech that infests ponds and streams, and which prefers to feed by swimming down the throat of anyone drinking the water so it can attach itself to the inside of the throat and suck their blood, incidentally suffocating them as it swells up. First appeared in White Dwarf's Fiend Factory series, in fact inaugurating said series; so, Classic Monster.

• Some bullshit called a "throat leech" appears in 5e's Tomb of Annihilation. This downgraded the horror to microscopic parasites that give you the exhaustion status effect. No, it doesn't count.

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  The classic "throat leech in the canteen" prank

Treant

An intelligent tree which will rip you to pieces if it thinks you're destroying the forest. Fortunately, they're technically good guys, so you won't usually need to fight them if you aren't actually destroying the forest (unless you're in Ravenloft, which has evil and undead treants).

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• Dark Tree: A malevolent counterpart to the Treant.

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• Noran: Another malevolent version of the Treant which lurks in underground environments. For added nastiness, they can also load rocks into their knothole and fire them out like a cannon.

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• Quickwood: Yet another evil version of the Treant, which attacks with its roots.

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Topiary Guardian

That bush trimmed into the shape of a lion is actually a lion.

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Tunnel terror

A huge stony psionic worm with a hollow body that pretends to be the walls of a tunnel to trick prey into walking inside it.

Umbral Blot (Blackball)

A construct with the appearance and properties of a Sphere of Annihilation. More of a "deterrent" gotcha monster, since a Sphere of Annihilation isn't something you should be messing with anyway.

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Vampire Moss

A mass of hanging, dense moss which passively drains the life force from any living creature that gets within 10 yards.

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Water Weird

That filled-to-the-brim water well in the middle of the desert you've been praying to Allah for? IT'S A SNAKE! OOH A SNAAAKE.

Wizard Lice

Blood-sucking insects that would be merely annoying if they didn't strip the spells right out of the minds of spellcaster hosts.

Wolf-in-Sheep's-Clothing

It doesn't look like a Sheep, and it isn't a wolf either. It looks like a small rabbit like creature, but that is only a small lure on top of its body, which looks like a tree stump.

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Xaver

A ferrovorous creature which disguises itself as a sword in order to get closer to unprotected metal.

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Hoard Scarab

A recent addition from 5E, but something at home with OG DND tricks. They are disguised as gold coins, and often found in dragon hoards. If you disturb them, not only do you have to fight off a swarm of locusts but PC will get covered in Glowing dust that not only renders all invisible useless but also pings all dragons in a 1-mile radius exactly where you are.

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Creed

A tactical geniu--Wait no, that's 40k.

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Gazebo

Beware the dread gazebo.

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Real Life Gotcha Monsters

To some extent, almost every ambush predator is a "Gotcha Monster". Just to name a few types:

• You have your "aggressive mimics", who pretend to be something edible, and turn around and eat those who would eat it; for example, several species of mantises and spiders looking like a flower (and sometimes waiting on one) and grabbing pollinators who show up, or the "alligator snapping turtle", whose tongue resembles a worm it can wriggle around to lure fish to it; the anglerfish uses a similar tactic, aided by a bioluminescent organ.
• There's trap-making animals, such as the antlion or web-making spiders.
• And then there's the camouflage and stealth approach, of which some varieties of cats are a common example.

The most likely one a D&D player (not character) might run into, are crocodiles and alligators; thanks to the old 'look like a log' trick. (Players, at least, don't worry about being dragged down to the depths in armor, like most of their adventurers.) This is why we stay indoors.