Librarianon

Inspired by @MabelGreysmoke's writings I've been musing on how Joule could work in a Hero/Villain world.

Powerset:
Joule harnesses the power of shadow and light, their dual tone fur pattern shifts to reflect which power is being used. Their powerset is largely defensive/traversal related, with limited offensive applications, making them ideal for espionage and sabotage.

Shadow Form: When the darker half is being harnessed it shifts to cover their entire form enveloping them in shadow before they "melt" into the natural shadows of their environment. They can only assume this form if already making contact with an existing shadow no matter how small or faint it may be. In this shrouded form Joule can move with great speed and stealth; provided there remain pre-existing shadows connecting to their destination through which to travel.
Gravity has no hold on them in this form allowing them to scale walls that are in shade or reach otherwise out of reach places. They can even use the shadows cast upon dust particulate or smoke to traverse in three dimensional space.
Shadow form's weakness is direct light, while shrouded Joule can be perceived as a slightly darker shade, as one might see when two shadows cross, though without the obvious objects or dual lightsources needed to naturally cause the effect. Should someone turn a light source directly upon them before they can evade the beam, the form is dispelled and they are temporarily¹ unable to revert.

Lightcasting: Lightcasting has three main functions Lightcasting (LC), Light Infusion (LI) and Lightburst (LB). The ability is contingent on having a pre-existing lightsource in direct proximity to Joule, though unlike with Shadow the light does not need to be directly cast upon them². Their white fur absorbs and reflects the light, overtaking the dark half of their coat until they are wholly aglow; can be as minor as giving off a glow by which to see (LC) or can be rapidly expended to create a lightburst; a blinding flash to disorient (as with a flashbang.) Though doing so will also burnout any local area (electrical) light source. And render Joule unable to perform further lightcasting for a brief period.³
Light Infusion is the practice of infusing an object of sufficient transparency and refraction with light, glass may be used, though faceted gemstones are more ideal⁴, these can serve to restore light to Joule for casting or be given to others to serve as small portable light sources in the absence of conventional alternatives.

Drawbacks: Items can be drawn into shadow form and moved therein however the density and mass of the object directly correlates to how long enshroudment can be maintained. For that reason Joule's clothing seldom includes metal, leather or hard plastics as their denser makeup limits Joules ability to maintain the form. Lightweight or low density object such as most forms of cloth and paper are easier to transform and can remain “shrouded” for greater durations, with repeated practice the length of time can be extended, though not without greater strain than may be worth the effort. Shadow form cannot pass through glass, there must always be an air gap between surfaces for the shadow to pass through.

While Lightcasting Joule remains solid and is vulnerable to any and all physical attacks. Using a lightburst will inevitably result in Joule suffering a crippling migraine shortly thereafter, rendering them incapacitated for several hours upto a full day. It is a last resort move.
Light Infused objects cannot be transferred or moved through shadow form, the natural density of gemstones and glass is prohibitive even without being infused, should Joule feel they will be required during a mission, small pouches of infused gems will be discreetly placed during a pre-mission scouting trip.

1. Mostly a disorientating tactic, as the method of pulling them from Shadow form by its nature creates shadows in which they may yet retreat if not apprehended swiftly
2. Direct light upon their fur increases the power of lightbursts, but is not needed for low-mid tier light casting.
3. There is a rough 30-40 minute window after a lightburst before the migraine kicks in, in that window Joule may force a second Lightburst if ample light is restored to the area and the need is great enough, but the damage to themselves is significant and they may be knocked out cold by the effort, compounding the ensuing migraine afterwards.
4. Light slowly leaks from vessels until expended, glass and clear gems leak the fastest, but hold more light initially, while darker and faceted gemstones hold less but hold it for greater periods of time.

further thoughts on this:
In a world where heroes and villains can smash through walls or shoot lightning from their fingertips, Joule has a great deal of anxiety relating to their powers, they're no fighter and the most they could do in combat is briefly stun an unprepared foe and then flee. They worry about being seen as cowardly or useless, a longstanding fear instilled by their father long before their abilities manifested. They prefer to work solo to avoid the (perceived) judgement of others.