Invisible characters present a tricky challenge in visual media: If the character is invisible, how can the audience follow what he's doing? To overcome this, creators have invented various methods of visualizing invisibility:
The invisible character is visible to the audience. No special effect required, just have the other actors pretend they can't see the invisible ones. Used often in live action, especially when the invisible characters are intangible as well (lots of ghosts are shown this way). Usually accompanied by some verbal cue ("They can't see us!"). It's common to cut to another character's POV to show he's seeing empty space.
The invisible character is rendered as a vague distortion of the background. A.K.A. the Predator method. Whether or not the other characters can see the vague distortion varies from work to work. This is also used quite often as transitional state, as when something switches its invisibility on or off.
The invisible character is partly transparent.
The invisible character is shown as an outline. Especially common in comics and animation.
The invisible character is completely invisible, even to the audience. Here, the only way to know what the character is doing is by indirect clues, such as the character leaving footprints, or walking through smoke or rain. If no such clues are given the exact position of the character is still often indicated by the camera remaining focused on them to the exclusion of everything else.
Chevy Chase in Memoirs of an Invisible Man, particularly when he was the only character onscreen. Other scenes had him completely invisible when needed.
When he's made invisible, it applies only to him and the clothes he's wearing at the time. He can don clothes to make himself visible, and quickly strips out of them in some instances when he needs to escape pursuers.
He's invisible to everyone including himself. He can see through his eyelids; he can see through the back of his head. Consequently, he doesn't sleep well.
Also, when he smokes you can see the outline of the smoke going down his trachea and entering his lungs. And when he drinks, you can see the juice going down his esophagus and enter his stomach. (Take his word for it: You do not want to see him eat.)
Which, oddly enough, made this the movie most true to the original book.
Heart and Souls, although Thomas Riley is the one person who can see the ghosts following him around, which makes him look insane to everyone else.
Amazon Women on the Moon has an interesting sendup: Ed Begley Jr. as the "Invisible Man", so he says he is, who is perfectly visible to everyone around him; they just play along with his antics. To make it more "authentic", Begley rips off all his clothes in order to carry out his pranks (sticking darts in the dartboard, stealing beer, etc). He's genuinely surprised when the police finally arrest him.
Claude in Heroes is visible to the audience most of the time during his episodes, but when he's introduced at the beginning of an episode, the audience hears his voice and sees him pick up an object, rendering it invisible. Also, the audience has seen him fade in and out of visibility. This causes his fans to believe that after he ran out on Peter, he's in every scene—we just can't see him.
Lampshaded by the writers: when asked if they were bringing Claude back, they replied "We already have. Didn't you see him?"
Al, in the Quantum Leap TV series, as a temporal hologram, is visible only to Sam (and occasionally animals and small children).
In the Buffy the Vampire Slayer episode "Fear, Itself", Xander turns invisible and unheard, playing on his fears of being ignored by his now college-going friends. Of course, the audience can see and hear him just fine.
In "Gone" however Blinvibl!Buffy is invisible to the audience as well. Buffy has fun showing off via talking skulls and baseball eyes.
In the Star Trek: Enterprise episode "Vanishing Point" Hoshi becomes invisible to the rest of the crew, but looks exactly the same to the audience, except when she looks in a mirror.
Shakespeare's original manuscripts have minimal stage directions, so when the ghost doesn't speak it's valid (if uncommon) to use the "Invisible to Audience" method below.
Stagehands in traditional Japanese theatre often dress in a black outfit covering their entire body. The "invisible" part comes in when you consider that this is where the stereotypical image of a Ninja came from - ninja characters would wear the stagehand costume when hiding to signify that the audience was supposed to ignore them.
Comedian-magician Mac King pokes fun at this trope with the "Mac King Cloak of Invisibility," a device that supposedly renders him completely invisible to whoever's on stage with him at the time as well as the audience. Said device is a bright yellow rain slicker that can practically be seen from orbit.
In LARPing, it's a common rule that a player can signal that he's invisible by holding his forearms crossed. Of course, this works on the honor system - it's up to the other players to play fair and act as if they don't see the invisible one. Or, for that matter, not use the signal unless their character actually can turn invisible.
Averted in the movie, and occasionally in the series. In the movie you can only see the disturbances that a cloaked character causes, like footprints, falling objects, etc. In the series you can see distortion sometimes, but not always — usually when the audience shares the perspective with the invisible character. There's always distortions for a few seconds when a character turns invisible, though.
The Invisibility power in Champions has a "fringe" by default. Another person has a chance to sense that fringe if they're within two meters of the Invisible character. You can buy your Invisibility with "No Fringe" for extra points, or make the fringe easier to detect to lower the cost.
Doom has spectres (and players using "partial invisibility") appear as a darkened silhouette.
Dystopia's stealthers are rendered as a watery distortion while they're moving, but invisible while they're still. TAC scans show a snapshot of their IFF boxes, and the Sound Wave Triangulator shows spinning triangles for their footsteps and gunshots.
Fellow Half-Life 2 mod, Neo Tokyo, has its own variant for the Recon class, appearing as shadowy silhouettes if you looked close enough. They were worthless if a player was using them moving or out in the open, but in front of things that broke up their outline, such as rows of boxes or vehicles, they were barely noticeable.
In Oblivion, the "Chameleon" magic effect is a partial subversion: as Chameleon strength increases, the distortion effect gradually gives way to full invisibility, and 100% Chameleon makes you both completely invisible and untargetable by the AI.
In the Halo series, the Active camo can be perceived as a player shaped distortion similar to heat distortion if you are close enough.
Jedi Academy has some high-ranking stormtroopers use this. The hilarious part is that they're usually still painfully visible, and the fact that they won't move or attack while cloaked means they'll just stand there and wait for you to impale them with a lightsaber.
Same with the Shadow Troopers in Outcast, but not as easy to impale them with the saber if it wasn't for the fact they were wielding one themselves.
In Kingdom Hearts, one Heartless called Stealth Sneak can turn invisible, having this effect.
Infiltrators using their tactical cloak, and Geth Hunters in Mass Effect 2. Unusually, the glowing "eye" on the geth is still clearly visible, which substantially undermines the effectiveness of the camouflage. Their cloaks are better in Mass Effect 3, but still not perfect.
The Metal Gear series, when a character is using stealth camo. The amount of distortion differs between NPC's and the player characters—a stealthed boss will be completely transparent aside from the distortion around the outline, while Snake or Raiden in stealth mode will also have a distinct green tint so you can at least see yourself. In Metal Gear Online, a sharp eye for these can help in stealth team battles.
Perfect Dark has the Cloaking Device, which leaves a faint distortion when the user moves around.
Enemy cloaked units in StarCraft have a slight distortion: it's very difficult to make out a Dark Templar who looks like a smoke trail. And even if you can see where he is, you can't shoot at him anyway. Once you know where the unit is though, you can move a detector there.
However, note that the attacks of a cloaked unit remain perfectly visible, which is a bit of a giveaway to a human player. Said human player will probably drop a Psionic Storm, ComSat Sweep, or Ensnare on the offending units.
The Ghost's attack is very hard to spot though, as it only gives off a small muzzle flash.
In The Hidden: Source, a Half-Life 2 total conversion, a team of players must hunt down the mod's namesake(while he is hunting them), who appears like this.
Used in Star Trek Online for the "Stealth Module" ground skill. Only teammates can see the distortion, to enemies it's totally invisible. Accompanied with an Invisibility Flicker when attacking.
Super Smash Bros. Melee uses this, when the character uses a movement to guide the player to know where it is; otherwise the character is completely invisible.
In Team Fortress 2, the cloaked Spy is visible as a distortion to his own team, but completely invisible (unless he's shot/bumped into) to the other team.
Unless he's using the Cloak and Dagger. That works normally when charged or when standing still. If the charge runs out and he moves, the same visibility effect happens as when he is shot.
Also, the Dead Ringer. If you have it activated before you get shot, you will don a perfect cloak (no flicker effect even if you are bumped into or shot again). The cost? The perfect cloak only lasts about 6 seconds and has a very loud and obvious "decloak" sound effect.
At one point in Mountain of Faith, the kappa Nitori shows up in "OpticalCamouflage". However, she's not really all that invisible; just translucent. The heroines point this out after they break the camo entirely.
In Prince of Persia: Warrior Within, there are "invisible" enemies that distort the image of whatever is behind them, and this distortion gets stronger at the edges, almost giving them an outline. Imagine a human-shaped glass figurine and you're pretty close. Only, light doesn't reflect off these guys, making them way harder to spot than glass.
The Nanosuit cloaking device in Crysis works this way. Unlike in, say, Metal Gear Solid, this means that enemies who are at close range or have already been alerted to the player's presence will, in fact, be able to see (and shoot) you. Likewise, it is possible to see cloaked enemies as well, if you look carefully.
The cloaked ninjas in Sensory Overload are this type, and are invisible to the Enemy Detecting Radar. They also usually reside in dark rooms, making them near-completely invisible.
Active Camouflage in Battlefield2142 used two methods, an earlier "Predator" method with a refracted outline that proved quite visible at a distance, and a later "static" effect that was more visible up close. Users were never meant to be completely invisible; limited charge, a shrill sound, and vulnerability to detecting gadgets ensured that they weren't completely undetectable by alert players.
Adaptive camo in Ghost Recon: Future Soldier appears like this. Like Crysis, it's not perfect (your character's exposed forearms are still pretty visible in the first level you get it in, for starters), but it's pretty close - enemies from further than a few feet will generally be unable to see you, even if they've been alerted and are firing on your teammates, but the downside is that you can't use it while walking upright, and firing a weapon or being shot at deactivates it.
In Keroro Gunsou, Keronian technology can make it so that specific people can see you while others can't. If you can see a cloaked Keronian, you see them as translucent images. The anime adds a rainbow glow to the outermost outlines, though it can get a little inconsistent with some items only having the rainbow glow.
Magical Girl Lyrical Nanoha StrikerS uses this method to portray Garyuu's and the Type IV Gadget Drone's invisibility, though attentive viewers may notice that the latter also used the Distortion method a few seconds before it made its presence known to the audience.
Rogues using stealth in most D&D-based video games, including Baldur's Gate and Icewind Dale.
BioShock: While you're standing still with the Natural Camouflage tonic equipped, your hands and guns are transparent.
All characters with Flash Steps in the DS Bleach fighters are shown as turning transparent and dashing to the specified direction to the user of the said character, but disappearing entirely and appearing elsewhere to the opposing player. Does not apply to actual teleports, which a few characters possess.
All stealth units in Command & Conquer: Tiberian Sun (completely invisible to the enemy, of course).
Ecco the Dolphin , in Defender of the Future, is see-through with stealth, but the enemies can't see him, even if he bumps into them.
Some ports of Doom I and II render Spectres as Demons with the transparency turned up.
In The Elder Scrolls IV: Oblivion there are two kinds of invisibility: regular invisibility and chameleon. Regular invisibility uses the transparent effect, unless it's another character using it, in which case they go completely invisible. Chameleon also uses partial transparency, whether it's on your or another person. However, if you reach 100% chameleon, you are completely invisible, even to yourself. This is an infamous Game Breaker, since regular invisibility goes away when you attack, but chameleon doesn't, and with either in effect, NPCs and enemies won't even try to find you.
EVE Online ships with cloaking devices are semitransparent to the player controlling the ship and completely invisible to everyone else, including teammates.
In Warcraft III, your own and allies' invisible units are partly transparent, but completely invisible to the enemy (unless they have invisibility-detecting), but you can still get them with splash damage. Then there's that unfortunate Invisibility Flicker...
In World of Warcraft, stealthed rogues, druids, night elves, and pets are shown like this. Stealthed enemy characters are completely invisible unless they come too close, though.
In Rise Of The Kasai, Tati and Grizz become shadowy and transparent when they stay still and hug the wall. The player can still see them, but enemies will walk right by without noticing them, allowing them to kill them from positions the other playable characters can't.
In City of Heroes allies who are cloaked will be invisible to the enemy but semi-transparent to you. Your character will also appear semi-transparent to indicate to you when cloaked.
A few stealth powers, like Cloak of Darkness and Shadowfall, make you look more like a cloud of smoke to yourself and your allies.
Oddly, not only will he be undetected by enemies, but he also passes through lasers (of the Laser Hallway variety only) as if they aren't there, and this is necessary at at least one point (when looking for all 20 of the casino chips in BINGO Highway, as the last one is behind some lasers).
The active camo in Halo: Reach. The user's transparency decreases when they move.
The Hobbit used this technique when depicting Bilbo using the Ring.
In BIONICLE 2: Legends of Metru Nui, when Vakama is seen after discovering his Kanohi Mask Power, he is completely invisible to the raging Makuta, however the viewer can see him quite clearly as a see-through, colorless figure.
Characters in Final Fantasy VI who have had the Vanish spell cast on themselves are shown as a black outline; Vanished enemies fall under the "completely invisible" format.
In the second Master of Orion, ships with a Phasing Cloak device equipped show up on the tactical screen as a transparent outline. You can scan a ship using their Phasing Cloak, but are unable to target it for weapons fire.
Used in Temple Run. Interestingly, the monsters can still see you while you're invisible, but it does protect you against trees and pitfalls. One can only guess that the invisibility makes you intangible, and that the monsters are quite supernatural. (Well, they do have skulls for heads.)
Danny Phantom, when invisible, is still inked in blackline but is given an airbrushed glow effect and filled in with slight white. Also, his eyes are drawn normally even when he's invisible to make it easier for the viewer to spot him.
Though averted with villains occasionally. They will be completely invisible to the audience if we aren't supposed to see them.
From the same creator: In The Fairly OddParents episode "Timvisible", when Timmy wishes for invisibility, a magic pencil's eraser tip rubs out all of his colors, leaving only an outline that, for some reason, only the audience is able to see.
Space Ghost: Jan and Jayce all were drawn in white outline.
Spoofed in an episode of Rugrats. The group becomes childhood expies of a Fantastic Four expy. While it's implied that the adult in the cartoon they were watching becomes fully invisible, Lil, being a baby, does not understand the reason for the outline and becomes "Dotted Line Girl" who unfortunately can be seen because:
Saber's invisible sword in Fate/stay night. Used to try and confuse enemies, though most Servants are skilled enough to see through the feint. Assassin almost perfectly describes Saber's arming sword, after which she drops the act.
Harry Potter. The footprint method is used in the third movie when Harry wears the cloak outside while it's snowing. However, in any shot where he's putting on or taking off the cloak, it falls into the category of distortion due to the use of the green-screen technique to make the cloak appear invisible.
The title character of Harvey is present only through his action on the environment, such as moving books.
Hollow Man — even his vomit was invisible. Plenty of tricks were used to still get a view of him though.
The Lord of the Rings trilogy, with Frodo. The only way we could tell where he was in the last part was by his footprints.
Bilbo was invisible to the audience while wearing the ring. However, when Frodo wore the ring, we saw a distorted version of reality with him in it.
When we finally get to "see" Invisible Boy's power in Mystery Men, he vanishes completely from the scene, only showing the objects moved by him.
The demonic presence in Paranormal Activity makes itself visually known by moving the bedroom door and the planchette on a Ouija board, shifting the bedcovers, or dragging the female lead out of bed and down the stairs. Later on, they dust the hallway floor with flour, and it leaves white, bestial footprints. (It has other tricks as well.)
The titular Petes Dragon can make himself totally invisible; the audience only sees his effects, like a petticoat being mischievously hooked on a nail.
The 2000 series — the camera would usually cut to Fawkes' POV to show what he was doing.
Somewhat lampshaded in one episode, where Darian has to spook out a superstitious generic South American dictator by pretending to be a ghost. His narration actually says that people aren't afraid of what they don't see, so if he's going to freak this guy out, he'll need to see something. Cue Darian letting the quicksilver drop from his eyes, to show human eyes looking out of nothing. Effectively creepy.
In a case of Special Effects Failure, the original The Invisible Man film starring Claude Rains had him leave shoe-like prints in the snow, despite the fact that he wasn't supposed to be wearing any. Stagehands made the footprints by pulling cutouts from a floor/boards that had fake snow on top, and it's easier to cut out a shoe shape (since usually in a bare footprint the toes leave separate prints).
Cloaked ships and characters in Star Trek and the Stargate Verse. Though early cloaked ships sometimes produced a distortion effect, which was actually a plot point (see the Star Trek III example; by the time of Star Trek VI the technology had been improved enough to eliminate the distortion).
Clara of Sanctuary used the footprints method of tracking usually, using the outline when she was 'found' by turning on the sprinklers. Later uses enabled her to partly 'uncloak' some part of her body to alert the viewers where she was.
Sam Casey of Gemini Man turns completely invisible, though the viewer is given clues to his presence by things such as bumping into other objects, chairs depressing from where he's sitting, objects he's holding floating, etc. This often just looks cheap, especially when the writers clearly have no idea of scale. For one example, Casey, while invisible, is holding a gun that to the viewer appears to be floating. When the henchman is staring down the barrel at it (thus a reasonable distance from Casey), he is suddenly punched in the face by Casey in spite of the gun staying perfectly still...thus somehow Casey punched a man with a six foot arm.
The third boss in The Legend of Zelda: Phantom Hourglass - you have to shoot it in the eye to make it visible again. Conveniently, the top screen shows the boss' first-person view of the fight.
Using the Invisible ability in Soulcalibur IV renders your character invisible, even to you the player- all you can see is the effects when swinging a weapon. Of course, this is because it's usable in Special Versus, too, and human players aren't so easy to fool as the AI.
The Illwrath ships in Star Control 2 have this as their special ability. However, since the "camera" is always aimed at the point directly between the two fighting ships, you can get a pretty good idea of where one is hiding.
Some NPCs in World of Warcraft have an ability that makes them invisible. The only way to see them is to wait until they attack (when the spell breaks) or use a detect invisibility spell. Mages also learn an invisibility spell, that causes them to turn progressively transparent until they disappear completely (it last for a very limited time, though).
If a ninja does this in Samurai Shodown, you may see flickers of him when he performs a manoeuvre. Less useful for Galford, since his dog Poppy always stays nearby.
Kopaka in the BIONICLE web-animations, when donning the Mask of Concealment. Only the footprints he leaves in the snow can be seen.
In Kickassia, Linkara remarks to interviewer Chris Larios that JewWario is extremely good at camouflage, and the camera pans to where the character is supposed to be standing. His disembodied voice is heard, and at one point someone bumps into him. Oddly, this ability is never used at any other point in the film.
Invisibo, from Freakazoid!, was invisible except for the scepter he always carried. Freakazoid still had trouble finding him, mostly because he's, well, Freakazoid.
Due to budget constraints, however, Invisibo appears for most of their first fight as a rod clearly dangling from a piece of rope. Yes, in a cartoon. Fortunately, due to how bad that looked, the producers let them have a higher budget about halfway through the fight.
"The Invisible Monster" in Jonny Quest left burning... er... blob-prints where it "stepped" and blew up anything it touched, so there was a clear delineation of where it had been. How Dr. Quest and Race were able to make it visible by dropping paint balloons onto it is never explained.
In the Phineas and Ferb episode "Don't Even Blink", objects and people hit with the Invisinator are completely invisible to the audience, except when Perry and Doofenshmirtz are hit off center and rendered only half-invisible—vertically.
Some fans say this is due to the dispersal of the beam. it's highly concentrated when up close and spreads into less visible beams the farther it gets from the source.
There's a Tom and Jerry cartoon, "Of Feline Bondage", where Jerry drinks an invisibility potion and becomes invisible, seen only by his shadow or when he held things.
Mirage in The Transformers. He turns invisible with an effect that looks like he's being surrounded with a laser cube, then the viewer only sees footsteps or items he's carrying.
Ravage in Beast Wars was not only able to turn completely invisible, save for his laser blasts, he was also able to turn his entire ship and everyone on board invisible.
In the Sponge Bob Square Pants episode "Pranks a lot," Patrick and Spongebob paint themselves with invisible spray, making them completely invisible to the viewer. This does not interfere with the camera panning between them and zooming in dramatically on the characters' faces.
Also in Spongebob, in one episode that parodies several superhero groups, Sandy gains a suit of invisibility. While trying to get around the villains because the other heroes got defeated, she gets hit by a boat and falls off a large cliff because nobody saw her.
Bugs Bunny in "Water, Water Every Hare" when he becomes invisible; the only giveaway besides flying items is the munched-up carrot that he eats.
Wile E. Coyote, thanks to invisible paint. All that's visible are his footprints in the dirt—unfortunate for him when he walks onto a highway and is creamed by an oncoming truck. After that the tracks become noticeably staggered, until he wanders dazedly off a cliff and smashes several Coyote-shaped holes in the clouds as he falls.
During an episode of Dave the Barbarian, the family has to defeat a group of "Invisigoths," invisible warriors that drove the people out of a neighboring kingdom. Reasoning that the Invisigoths can see each other, Uncle Oswidge turns everyone invisible to the audience, leading to a rather humorous sequence where the audience hears the fight, and the frames are edited to highlight the fight, but we still can't see what's going on.
Multiple methods / Other
Anime and Manga
Ea from Toumei Shoujo Ea (English title: "Invisible Girl Ea") takes all the methods, for the most part. She shifts between visibility and invisibility to the audience, except when her powers are malfunctioning, wherein she distorts like the predator or shows up as a translucent blue ghost.
Similarly, Shizuka in Translucent uses several of the tricks. The story focuses on how Shizuka has contracted "Translucent Syndrome", a nonfatal, noncontagious disease that turns her mostly translucent on a monthly cycle. In the manga, this is shown via either sketching in the background lines behind her, showing her without any shading at all (or as a very pale gray), or showing her without any lines at all (merely using shading). People who get more serious versions of the disease can end up with "Fully Transparent Syndrome", which is traditional Invisibility stuff — which in the manga is shown by the "completely invisible, even to the audience" subtrope, with the exception that extreme positive emotions can cause a faint screentone outline to appear. The one character who has FTS in the series wears a hat, gloves and glasses to show people where her head and arms are.
The title character of Kasumi can turn invisible whenever she holds her breath, and has been seen as all types (exceptBackground Distortion), at some point.
In a Post-time skipfiller episode of Fairy Tail, Lucy turns invisible after bathing in some potion which had gone off (having been unused for 7 years). For the most part, she is completely invisible, with the audience only being able to see the towel wrapped around her, and is occasionally Distorted Background (with very faint glow surrounding her). She is also at one point after being completely wiped from existence fully visible to the audience, but everything else is covered in a purple haze.
The Blitz Gundam of Mobile Suit Gundam SEED tends to bounce around Distortion and Completely Invisible when it uses its Mirage Colloid stealth device. Like the Kim Possible example below, how it's shown depends on what's going on. This also goes the same for other machines that use Mirage Colloid.
Over the course of fifty years, Susan Richards from the Fantastic Four has had her powers portrayed in every method but the first. The original Silver Age comics used outlines; the movies used Predator-style distortion; and later comics, cartoons, and video games have alternated between partial transparency and total invisibility, Depending on the Artist.
In The League of Extraordinary Gentlemen, invisible man Rodney Skinner is completely incapable of being seen in most instances. When he wants to be seen, he dons a trenchcoat and/or slathers greasepaint on his face. Done to great effect in the Mongolian blizzard scene, where he is visible only because of the snow landing on his head and shoulders.
In Memoirs of an Invisible Man, the title character is visible to the audience in several scenes where he is invisible to the other characters, mainly for a bit of Dramatic Irony, but in many scenes he wears fully-covering clothing or makeup. Several notable scenes have him distinguishable only by the rain falling on him, the smoke from his cigarette in his lungs, or the partially digested contents of his stomach (which he vomits up when he sees this last).
Live Action TV
On Misfits, Simon alternates between visible to the audience and totally invisible.
In Psychonauts, there's a red glow where Raz's eyes would be in order to show you where he is. This is supposed to represent his goggles, but in the real world, where he doesn't wear them, it looks a little strange.
Hector the Reflector, a Yoshi's Island DS boss enemy, is invisible, but fights in an arena with a mirror in which you can see the boss reflected. He also smashes the mirror more and more as the battle goes on.
In Command & Conquer: Red Alert, cloaked units are shown as shadows to their general (copying the style of how submerged submarines are shown; indeed, there are normally no cloaking land units in the game barring bonus crates).
In Donkey Kong 64, you can see your clothes and shadow when invisible. You can see most invisible enemies' shadows as well.
King Boo in Super Mario 64 DS sometimes becomes kind of invisible in the boss battle; you can see him, however, via both his appearance in the mirror reflection and a shadow on the floor marking his location.
The Pokémon Kecleon can turn invisible, but the red zigzag stripe around its body can be seen.
However, it's implied that the red stripe left behind is nearly or totally invisible anyway, as none of the characters in the anime manage to spot it in an episode that featured Kecleon, even when it was around things that would make said stripe stand out.
In Quake I, the Ring of Shadows turns you invisible except for your eyes. Observant players will be able to spot this, while monsters will ignore you, presumably thinking you're a benevolent spirit... until you attack them, then they know to attack the floating eyes!
One of Wario's forms in Wario Land 3. The player must rely on the dust clouds kicked up by his feet when walking to track him, and he'll occasionally flicker for a few milliseconds as well.
Dexter in the Dexter's Laboratory episode "Surprise!" is shown as an outline when invisible. However, near the end, we see him from the viewpoint of a couple of kids and then he is completely invisible on-screen.
In an episode of The Flintstones, Barney accidentally gets turned invisible. He puts on a green hat so Fred can see where Barney is standing at any given moment.
In the episode "Mad Dogs and Aliens" of Kim Possible, Kim gets a stealth upgrade for her battle suit, which uses the distortion effect. However, it should be pointed out that when she actually sneaks into Drakken's lair she's completely invisible until she makes her appearance behind Doctor Drakken. It's zig-zagged between completely invisible and a distortion, depending on what's going on. Of course, it's stealth ability is only shown in one episode.