You're tearing yourself to tatters every time you go all the way to the eighteenth floor to mess with your old boss. There's an easier way. Lemme show ya...

Corporis allows the wraith to manipulate the density and properties of her corpus. It is similar to Moliate in this respect, and in fact, Corporis is a recently developed derivation of that Arcanos. But rather than focusing on the vulgar reshaping and transmogrification of the corpus, a Restless skilled in Corporis can affect the density of her wraithly body, becoming as insubstantial as smoke or as solid as stone... at least, in the Underworld. Though the effects of this Arcanos are generally limited to the Shifter himself, masters of Corporis can impart (or impose) arts on others. This Arcanos works well in conjunction with Moliate (which the Corporis Arcanos is based on), as well as with Phantom Wings (Argos ●●), as it extends the time the wraith may spend aloft. Wraiths who are material (by use of Embody) can't use Corporis; it affects only the corpus.
Not many wraiths suspect the existence of this Arcanos, and even fewer practice it. Nevertheless, since its introduction to the general wraith population in recent years, it has been gradually growing in popularity.

The Guild
There never was an official Shifters guild. Corporis was a side project of several Masquers, who developed it to enhance and refine their control over their plasmic bodies, and the spies and saboteurs of the Guild employed this Arcanos to great effect. Corporis was never widely practiced, and until only recently was the sole providence of a few Masquers. However, someone leaked knowledge of this Arcanos to outsiders, and is now practiced by a select handful wraiths throughout Stygia. The Masquers would very much like to find out who is responsible for this.
Shifters gradually develop a translucent quality to their corpuses, a side effect of dispersing their plasmic bodies so often; masters of Corporis often resemble smoky glass, marbled with streaks of "solidness."

Botches
Botches involving Corporis may cause corpus damage equal to the level of the art used, or the art may have opposite the intended effect; those who wish to solidify become insubstantial, while those who want to become incorporeal (or wish to maintain that state) suddenly solidify -- bad news for someone walking through solid rock. Or, a character may gain penalties associated with a corpus state without any of its benefits (for example, someone using Solidify loses Dexterity, but remains as vulnerable to damage as he is normally).

Basic Abilities
Ectoplasmic Tracking: When a wraith rests inside of a Fetter, or passes through a solid object which causes (or would cause) corpus damage -- a wall, a moving automobile, even a person -- she leaves a little bit of herself behind in the form of ectoplasmic residue. By staring at an object and making a successful Perception + Corporis roll, the Shifter can determine if a wraith has passed through or rested within it recently. The difficulty of this roll is determined by how old the ectoplasmic trail is: ten minutes (difficulty 5); one hour (difficulty 6); six hours (difficulty 7); twelve hours (difficulty 8); one day (difficulty 9). Ectoplasmic Tracking allows a Shifter to follow a quarry's trail through a building, and even get a general idea of the body mass of the wraith in question by the size of the trail left behind (three or more successes).
Note: People subjected to Puppetry and items subjected to Inhabit don't count as having been "passed through" for purposes of Ectoplasmic Tracking, though wraiths using these Arcanoi do leave a faint residue behind; this can only be detected within a time period equal to ten minutes per dot of Corporis, and requires a Perception + Corporis roll against a difficulty 9.
Prolong: A wraith's Corporis rating is added to his Stamina to determine how many turns he remains incorporeal after taking damage from a source in the Skinlands. The wraith may, at will, return to a corporeal state at any time while incorporeal.

● Incorporeal Extension
With effort, a wraith may remain incorporeal for longer periods of time. While this art doesn't protect the wraith from damage inflicted by sources in the Shadowlands, Incorporeal Extension is invaluable when the wraith must travel through many barriers or through dangerous conditions (such as heavy traffic). Incorporeal Extension is one reason why Shifters are spies and assassins par excellence, as they can easily enter and exit areas dangerous (or at the least, inconvenient) to other wraiths.
System: A point of Willpower plus a variable amount of corpus, and a successful Dexterity + Corporis roll by the player (difficulty 8), allows the wraith to extend the time he remains incorporeal; the wraith must be incorporeal to use this art. Each level of corpus spent (beyond the initial corpus cost to become incorporeal) converts one turn of incorporeality into one minute. For example, a Shifter with a Stamina of 2 and a Corporis of 3 normally remains incorporeal for five turns. However, if he makes a successful activation roll (above) and spends one Willpower and three corpus, he may remain incorporeal for three minutes, plus two turns.
The wraith employing Incorporeal Extension may return to his corporeal state whenever he wants to, but ends the duration of the power.

●● Solidify
By compacting and hardening his plasm, the wraith becomes more resistant to damage, though he sacrifices mobility and flexibility. The character may even become as immobile as a stature, though as resiliant.
System: The player spends rolls the character's Stamina + Corporis (difficulty 6), and spends one Pathos. Every success is an "autosoak", allowing the wraith to subtract one level of damage from any source before soak is rolled. Especially severe damage, such as that inflicted by the Outrage art: Obliviate, isn't automatically soaked; however, every success on the above Stamina + Corporis roll grants the wraith one soak die to avoid damage (when no soak would have been allowed before). Every two successes reduces the wraith's Dexterity by one (round successes up the nearest even number). For example, a wraith whose player rolls three successes while using this art gains three levels of automatic soak (or three dice), while losing two points of Dexterity. A character reduced to a Dexterity of zero this way can't move, speak or take any physical actions (and is precluded from making any rolls involving Strength or Dexterity) until the effect wears off or the wraith wishes it dispelled.
Assuming the Shifter doesn't voluntarily end the effects of this art, it lasts for one scene.

●●● Obscurement
While incorporeal, the Shifter can intensify the insubstantial quality of his plasm, making him indistinct and almost transparent. This allows him to move about unseen to most wraiths, and to disorient those who do see him. The art also deadens the sound around the character's feet, making it difficult to hear him. Obscurement takes concentration, and the wraith can't perform any action more complex than movement while this art is active.
System: The Shifter must be incorporeal to use this art. The wraith's player rolls Wits + Corporis (difficulty 7). Each success on this roll subtracts one success from others' die rolls to spot, hear, or (if detected) attack the wraith. If the wraith engages in any activity that requires his full attention (expressly including combat or athletic feats) the effects of Obscurement are dispelled.
Obscurement costs 2 Pathos, and its effects last until the wraith becomes corporeal, or he stops concentrating on maintaining the art's effect.

●●●● Tenebrous Form
Tenebrous Form allows the Shifter to assume a quasi-incorporeal form, becoming less substantial even to other wraiths. This offers protection from anything in the Shadowlands that would damage him, as most attacks pass right through his corpus; however, he is rendered equally unable to harm anyone else. Even more interesting and disturbing than this, however, is the ability to "corpus-ride" other wraiths! In many ways, this art is the opposite of Solidify, as the Shifter disperses his plasm rather than hardening it. The appearance of the wraith is unsettling: his form becomes an undulating humanoid mist, shot throughout with wan gray light.
System: The wraith must first be incorporeal to use this art. Another corpus level is spent (on top of that spent to become incorporeal), and the wraith's player must make a Stamina + Corporis roll (difficulty 8). If this roll is successful, the Shifter disperses his corpus. The Shifter's Corporis is added to all soak rolls against physical attacks, but his Strength drops to zero.
A Shifter in Tenebrous Form can actually enter the corpus of another wraith; this requires a Wits + Corporis roll, resisted by the subject's Dexterity + Dodge (if she's unwilling). Treat this ability as the Puppetry art: Skinride, except that it applies to wraiths instead of the Quick, and the "host" can kick the "visitor" out with an opposed Willpower roll (which may be made once every scene). Certain uses of Castigate arts may also force the Shifter out.
The Tenebrous Form lasts until the wraith desires the effect gone, or until he becomes substantial. When this power is used against an unwilling wraith, the Shifter gains one Angst.

●●●●● Imposition
This art is commonly used to share insubstantiality and Corporis effects with other wraiths (willing or no), and to impose their effects on inanimate objects. However, particularly vengeful or hardened Shifters have been known to use Imposition to yank mortals, hated Giovanni vampires and such into the Shadowlands, where they are at the mercy of whatever is there; though the visit is brief, that's often all it takes for the wraith's work to be done.
System: The wraith can impose an insubstantial state on a Skinlands resident with whom he is in physical contact; the wraith pulls the subject out of the Skinlands and into the Shadowlands. (Skinland witness will see the subject disappear before their eyes, which will definitely provoke the Fog.) The player marks a point of Willpower and three points of Pathos off the wraith's sheet, then rolls Strength + Corporis, difficulty of the local Shroud; an unwilling victim may resist this with a Willpower roll (difficulty 7). Each net success rolled for the art forces the subject to spend one turn in the Shadowlands; if the subject is being Skinridden, the possessing wraith is immediately forced out. During this time, the visitor is treated as a wraith for purposes of what and who can damage her (though as an incorporeal being, at least she need not worry about damage from the Skinlands). Mortals are fully under the effect of the Fog while in the Shadowlands, and will be scared witles and prone to all sorts of derangements after the experience (Storyteller's discretion). If Imposition is performed upon a willing subject (not likely), the Shifter gains one point of Angst; doing this to an unwilling victim inflicts two points of Angst to the Shifter.
Forcing an inanimate object to become insubstantial is not nearly so problematic. The Shifter's Manipulation + Corporis is rolled, difficulty 7, and one point of Pathos is spent. Success converts an object, or part of it, to insubstantial plasm in the Shadowlands. (This art has no effect on objects in the Skinlands). This is useful for allowing groups of wraiths to enter a building with little or no corpus damage. The successes rolled determine how much matter the Shifter can affect: a single success might create a spot just large enough for a wraith to crawl through the wall, while five success might affect something as large as a house trailer. The duration of this effect is equal to the successes rolled, plus the wraith's Corporis, in turns.
The Shifter may share, or impose the effects of, one or more the following arts: Incorporeal Extension, Solidify, Obscurement and Tenebrous Form. The character must be in contact with the wraith(s) with whom he wishes to share his art. The player rolls the character's Manipulation + Corporis (difficulty 6 + the number of subjects), spends one Willpower point, and burns one Pathos for every subject. Unwilling subjects can resist with a Willpower roll. The effects of the imposed art are determined by the Shifter's traits and point expenditures, and end immediately for a subject when she loses contact with the Shifter.
When any Imposition effect is imposed upon an unwilling subject, the Shifter gains two points of Angst.