Disguise

A disguise in the PPC is not merely a change of costume and a false nose; it is an alteration of form produced by a piece of technology called the disguise generator. Disguises are necessary for some field agents, especially assassins, to minimize any canon disruptions their presence or actions would otherwise cause.

How Disguises Work
When using a full disguise, an agent's body is physically transformed into whatever species they choose, with all its anatomy and physiology. For instance, when Jay and Acacia used the disguise generator to become Ents, their tree-ish bodies were not hurt by arrows.

Disguises can also be used in a more limited way to transform one's clothing into something canonical.

An agent cannot disguise themself as a specific named character, nor a species that is not canon to the continuum they are visiting.

The disguise does not affect the agent's mind, so they retain their own knowledge and will not necessarily know how to use a disguise's natural abilities. A human disguised as a dragon will not automatically know how to fly; they'll have to figure it out.

It also doesn't completely overwrite the agent's intrinsic characteristics or behavior. An agent who generally embodies the roughest of rough men may never quite pass as an ethereally beautiful elf. It certainly doesn't help if said agent actively drinks, smokes, curses, and innuendo-izes during the mission.

Similarly, a disguise will not necessarily remove any injuries, disabilities, or other health conditions an agent has in their normal body. Agent Somariel has to medically manage an autoimmune disorder that compromises her lung function so she can go on missions; Agent Ix remains infertile even using a disguise; Agent Derik always has some form of "Phantomy" facial scarring and partial blindness, even if he attempts to remove it.

This appears to be subject to the Narrative Laws, though, and varies per agent. Agent Aspen Green, who is normally blind, gains the visual ability of whatever she disguises herself as.

When They're Applied
By default, a disguise falls into place as soon as an agent goes through a portal into a Word World and drops when the agent crosses back into Headquarters. These settings can be changed with the remote activator (when the agents remember). As Acacia discovered when she forgot to remove an arrow from her Entish behind before going back to Headquarters, things that happen to an agent in disguise stay happened when they change back, so preventing an untimely shift between forms can stop a medical emergency from getting worse.

Disguises are not usually kept up long-term in Headquarters, even if they would confer some advantage. Aspen describes doing so as "really, really weird" and chooses to remain blind and navigate with her cane instead.

Using a disguise instead of making your own costume for a party is regarded as a breach of etiquette by some agents, but people who want to "dress up" as another species are given a pass.

Why Disguises Are Used
PPC agents are aware that they are as uncanonical as any original character in a fanfiction, and may disturb the continuum simply by their presence. Since the canon is already damaged by the Mary Sue, Sue-wraith, or general horrible writing that required a mission in the first place, it's important for the agents to avoid making it worse. They do so by disguising themselves as something that would 1) be where they are, and 2) do what they do.

Disguises aid the canon in cloaking the agent from the sight of the canon characters. For passive observers, such as Intelligence agents, the canon cloaking is less effective, so a disguise that fits in where the story is taking place (e.g. an orc in Moria or an elf in Rivendell) is advised, especially in locations that are less disturbed by the influence of badfic.

For active protectors such as assassins, however, using enemy disguises is sometimes a better idea than using "friendly" disguises (such as an elf in Middle-earth). Since most Mary Sues are "good" characters, it is more canonical for an assassin to use a disguise that would kill a good character in that canon. Most assassins will also use canonical weapons or other in-canon execution strategies to kill a Sue—not only is it satisfying to kill a Tenth Walker with orc arrows in Uruk-hai disguise, it's also a way of keeping the canon as intact as possible.

Forgetting your disguise or using an inappropriate one leads to bad things, especially if the canons are in-character enough to attack a "hostile" disguise (for example, when Jay and Acacia found themselves attacked by both the Sues and the canon characters due to being Ringwraiths ). Being seen without disguise by a Sue makes any mission much more difficult, as it becomes much more obvious that you're not just another background canon and it subsequently gets more likely the Sue will either try to escape or attack. Even the weakest Sue can be a threat to PPC agents with the right resources or incentive.