Trope Workshop:Stealth Mook

The average Mook in video games and other fiction is usually of the straightforward variety - you see them, they see you, fighting time, fighting time, blows are thrown. From large to small, regular mook to elite, all walks of life... most Mooks don't mince words about how they're out to mince you. But some of them are much more cloak-and-dagger about their business - their job is to ensure they remain unseen long enough to attain their objective, whether it's killing or otherwise defeating you, or else leading you away from your main objective.

These Stealth Mooks aren't always exclusively majors in hiding, and can easily overlap with other Mook types. For a Mook to qualify as one, though, the stealth must be one of their significant roles in a level or enemy party - whether or not the Mook elects to fight you varies. The sources of this Mook's stealth ability can range from being visible but hard to spot on-screen, to being completely undetectable until they attack; said abilities can be conferred by anything from magic or super-technology to Geo Effects, or simply being Genre Savvy enough (perhaps dangerously so) to use the terrain around them. Tougher Stealth Mooks may warrant special tactics and/or items to defeat.

Ninja are by far the classic and most common examples of Stealth Mooks, as well as a common subtype of Mook that actively avoids your sight until you draw near.

Compare Invisible Monsters, who are naturally tough to see regardless of whether they're actively sneaky. Contrast the Stealth-Based Mission, where you're the one trying to stay unseen by mooks whose job is to find you. A protagonist with stealth abilities is usually The Sneaky Guy in a party of playable characters, and often the main playable character in a Stealth Based Game.

Video Games

 * The Luigi's Mansion series has several ghosts that fit the bill:
 * In the original Luigi's Mansion, there are two subtypes of Grabbing Ghost that are normally invisible - one can only be seen via their reflections in a mirror, and another can only be detected by their shadows on a projection screen. They only become visible when grabbing you, though you can also reveal them with your flashlight or elemental attacks from the Poltergust.
 * Luigi's Mansion: Dark Moon has Sneakers, who turn invisible to scare Luigi from behind and interrupt him capturing other ghosts. Luigi's Mansion 3 has the similar Slinkers.
 * The Bloons Tower Defense series has the Camo Bloon, which first appears in Bloons Tower Defense 4. In its initial appearance, it is around the same level as Black and White Bloons, and can only be actively targeted by a tower or monkey with camouflage detection - they can still be hit and popped by collateral damage from area-of-effect attacks. Bloons Tower Defense 5 and 6 make Camo a "trait" applicable to any non-MOAB Bloon, and Camo Bloons cannot be targeted or damaged by towers without camo detection.
 * Fool Eaters from Hollow Knight are giant carnivorous plants that lie in wait for prey, hiding their open jaws among the heavy foliage of Greenpath. Once you step on them, you've got maybe a second to get the hell out of dodge before it bites you, and the only warning you get is a faint rustling sound.
 * Stalkers from Horizon Zero Dawn are deadly ambush predators, utilizing cloaking technology while hunting their prey. Even when you go into places that are identified as Stalker territory on your map, chances are you won't find them. They'll find you, likely because you triggered one of the alarm mines they've got laying around, or bumped right into one of these invisible menaces while trying to find a patch of tall grass to hide in.
 * The Assassin's Creed series naturally has its share of them.
 * Assassin's Creed: Revelations and Assassin's Creed Rogue have Stalkers, mooks that blend into the civilian population and attempt to Back Stab the player character. They can be revealed with Eagle Vision.
 * Pokémon video games:
 * Pokémon Gold and Silver and their Gen 4 remakes feature an unusual variant: The Fuchsia Gym Trainers all disguise themselves as their leader Janine, who has taken over now that her father has become an Elite Four member. In order to unmask the real Janine, you're expected to talk your way through the gym, which means fighting her Gym Trainers - however, Janine always waits in the same spot, making it trivial to skip them if you're so inclined.
 * Pokémon Ruby and Sapphire introduce the Ninja Boy trainer class, who disguise themselves as various objects in the overworld like trees or ash piles to ambush passing trainers.
 * The cipher Peons from Pokémon Colosseum and its sequel, Pokémon XD: Gale of Darkness, aren't always visible in the overworld like most enemy trainers. When you step into their aggro radius, these stealthy ones will jump down from the ceiling and ambush you. One even ambushes you right after you use a cramped elevator, and follows you out of said elevator despite not following you in.
 * NetHack and its variants have various monsters such as snakes, cave spiders, piercers, and trappers that can hide themselves from view, and usually wait until you are close to strike. You can reveal them by searching manually, and warning or telepathy will alert you to their presence.
 * The Samurai quest plays on the samurai-ninja contrast by including actual ninja and invisible stalkers among the more common hostile monsters that you'll encounter - the ninja themselves tend to avert this, however, with the stalkers being harder to detect in comparison.
 * In SLASH'EM and variants of it, gnolls are adept at hiding to the point that warning cannot detect them - telepathy is the only way to spot a gnoll before it ambushes you, and stronger types of gnoll can generate with some powerful armor and equipment.
 * dNetHack include the Garo from The Legend of Zelda: Majora's Mask, who use the same glyph as normal floor tiles, making them difficult to spot.