A Portal 2 mod, later released through Steam Greenlight. Aperture Tag swaps out the Aperture Science Handheld Portal Device for the Aperture Science Paint Gun, a gun that shoots the Propulsion and Repulsion gels. Armed with the ability to paint virtually any flat surface with mobility gel, the player is presented with a range of new puzzles, including puzzles from Portal 2 that must now be solved with the new mechanics.
Set after the first co-op campaign of Portal 2, Aperture Tag casts the player as one of GLaDOS's new human test subjects and contains a full-length single player campaign. Accompanied only by your test supervisor, a personality core named Nigel, the player has to work through yet another one of Aperture Science's testing tracks.
The game also includes a built-in level editor with Steam Workshop support, similar to Portal 2's Perpetual Testing Initiative, allowing users to create and share new test chambers with others.
This work contains examples of:
- Ambiguous Gender: While the player character seems to have a somewhat feminine figure, unlike Chell they're never confirmed as such outright.
- Ambiguous Ending: In the final scene of the of good ending, the field the player character enters is revealed to be fake, with them presumably still being within Aperture. The implications this has on their ultimate fate are not clear.
- Anti-Frustration Features: One part of the game requires a 50 second string of lightning-quick reflexes with choosing and shooting the gels—one slipup and you're dead. If this is too frustrating for you, you can press a button on the wall to view the segment as a cutscene instead.
- Artificial Outdoors Display: Several of the later test chambers are painted to resemble outdoor scenes, at least on the still quite obvious walls and ceiling. This doubles as a bit of Foreshadowing, as in one ending of the game the player steps outside, discovering that they have walked into yet another fake, though slightly more convincing (until it starts falling apart), large outdoor scene.
- Big Bad: Nigel is a particularly non-malicious example so it's hard to tell at first, but he's still the main force behind everything the player character goes through and attempts to murder them near the end.
- Black Comedy: Developer commentary states that Citranium having the -ium suffix wasn't just to make it sound like an element - it was to imply the drink was radioactive.
- Brick Joke:
Nigel: Remember when I said we were not going to recycle old test chambers? It turns out I was wrong! Haha, have fun!
- Midway through chapter two, after the player has completed several chambers from previous games with the new mechanics, Nigel cheerfully announces that there will be no more reused tests from here on out. Several test chambers later the player arrives at the beginning of chapter three, which is even titled "No More Test Recyling." They then immediately walk into the chamber "Column Blocker" from Portal 2.
- At one point in the game, Nigel says you will get a free can of Citranium once you've completed the test. Turns out, the vending machines are all out, but Nigel assures you that he will personally make sure you get one at the end. And at the just before the finale, dozens of cans are launched at you from Pneumatic Diversity Vents.
- The Cake Is a Lie: Played with in regard to the can of Citranium Nigel promises you. The vending machines at the end of the chamber are all out, but he promises to give you the Citranium later. He eventually makes due on his promise...right before an Emancipation Grill leading to a deadly fire pit.
- Comedic Sociopathy: Nigel makes quite a few comments about the eventual fate of all the test subjects.
- Downer Ending: The default path ends with the player character being burned alive at the end of the final test. Nigel even attempts to call upon a "loophole" he suddenly remembers to save the player from this fate, but by then it's far too late.
- The Ditz: Nigel is incredibly friendly but can be quite absentminded and is generally oblivious at times, though fortunately his obliviousness only occasionally gets the player into trouble. This gets you killed in the Downer Ending, since there is apparently a loophole to the "kill the test subject" requirement he could have used to save you from the firepit but he remembers it far too late.
- The Determinator: The protagonist is implied to share this trait with Chell. Them managing to escape death prompts GLaDOS to notice this similarity, and promptly allow them to be freed.
- Escape from the Crazy Place: Run the tests so that you can hopefully find a way out seems to be the main plot of the game, though we aren't sure of the player character's exact motivations. Aperture Science is still about as crazy as you can get.
- Everyone Lives: Disregarding the dozens of turrets you have likely slaughtered, at the end the game the player steps out into the sunshine and Nigel goes back to his job. As long as you get the good ending, of course. Otherwise the player character is dropped into the incinerator at the end of the game. Oops.
- Foreshadowing: At one point, Nigel notes that the tests look fun and he wishes he had legs so that he could try them too. He then immediately remembers the other, more deadly things that tend to happen to test subjects. Guess what happens at the end.
- Featureless Protagonist: Averted. Despite the smaller number of portals, there's at least one pair that are arranged so that you can see you resemble Chell, but with an apron, a blue shirt, and red hair.
- For Science!: As with most of Aperture's products, there doesn't seem to be any practical purpose to the gel test chambers. Why is the player running this deadly maze? Because science!
- The Ghost: Characters from the canon Portal series don't appear beyond being occasionally referenced by Nigel, and even then they're never outright name-dropped.
- Greater-Scope Villain: From the perspective of this game's story, GLaDOS is this, being directly responsible for most of it but only being offhandedly mentioned as Nigel's boss from time to time.
- Heroic Mime: Once again, Aperture has managed to find a mute test subject. One wonders if they pick them out specifically.
- Karma Houdini: Nigel is not punished in any capacity for attempting to murder the player character in either ending, and presumably simply continues doing his job unharmed.
- Level Goal: In place of elevators, this game makes use of the Pneumatic Diversity Vent, now called the Aperture Science Vacuum Delivery System, to carry the player between test chambers.
- Leaning on the Fourth Wall: At one point, Nigel repeatedly references the use of 'reused test chambers," obviously nudging to the fact that that these levels used reused maps from Portal 2.
- Minimalist Cast: The game contains only two characters of note; the unnamed player character and the personality core Nigel, who serves as guidance.
- Mission Control: Nigel's main job through the plot is to walk the player through testing protocol. He doesn't help with test solving, beyond basic controls, but he'll often inform the player of goals that might not be obvious, particularly when they're outside testing areas.
- Multiple Endings: Two possible endings, the first of which is where you die in a fire like Chell was supposed too. The second ending is where you sneak out of the last chamber, deactivate the fire, complete the test chamber, and get freed by Nigel when he finds you've survived the finale.
- No Name Given: The player character's name is briefly discussed, but never explicitly revealed.
- Product Placement: In-universe, one test chamber has advertisements for Citranium all over the place, and Nigel promotes it regularly throughout chapter 4.
- Punch-Clock Villain: Nigel. He doesn't really want the player to get hurt and takes a genuine interest in their well-being, though he doesn't do anything to stop the increasingly dangerous situations the player finds themselves in and pretty much just does his job, including allowing the player to die at the end if the player has not already intervened. He does however attempt to save your life by invoking a 'loophole' he suddenly remembers, but by then you are already in the pit burning away. He is, however, happily and pleasantly surprised if and when the player survives.
- Pragmatic Villainy: This is heavily implied to be the reasoning behind GLaDOS' ultimate decision to spare the protagonist in the good ending, due to their resemblance to Chell making them not worth dealing with.
- Punny Name: Your supervisor is Nigel, a pun on the gel that makes up the core mechanics of the game.
- Puzzle Game: Solving the test chambers is pretty much all you're doing.
- Sesquipedalian Loquaciousness: We get to see yet more of Aperture's verbose naming tenancies; the Aperture Science Cold Work Apparatus ("The Crusher"), the Aperture Science Vacuum Delivery System, and the Aperture Science Paint Gun and Aperture Science Paint Gun Activation Field. Turns out there is an AI who's whole job is to name the Aperture Science Patented Devices. (He came up with that name, too.)
- Shark Fin of Doom: One level has a monitor showing Nigel in a fake ocean, surrounded by sharks.
- Source Music: Music comes from speakers installed on the testing track. It malfunctions in one test.
- Spikes of Doom: With propulsion gel as a vital puzzle component, it's not surprise puzzles utilize it to get past giant spiked crushers.
- Toilet Humor: Almost all secret areas have a toilet in them, and going near them results in Nigel commenting on your weak bladder. This was meant to be a build up for the last chamber, where you had to access one of these areas in order to get to the incinerator control room.
- The Unfought: Unlike other Portal antagonists, the player never attacks Nigel directly, and the closest they come to opposing him is disabling the trap at the end, which he's actually more relieved about than anything.
- We Have Reserves: The player is one of the thousands of test subjects discovered at the end of the co-op campaign. This could explain the increased lethality of the gel chambers compared to traditional portal chambers; what's the death of one human when you can just throw another one into the chamber and continue the testing?
- You Monster!: Parodied in one of the developer commentary nodes about using Nigel's electrified rails to cheat:Harry Callaghan: You can still use a shortcut in the chamber if you are quick enough. I mean, erm no, shortcuts are bad and you should feel bad. You monster!