Alright! The IC is ready! I'm sorry it's a bit long, I was trying to establish what exactly it would look like when a Shadow attacks. Hopefully everything was explained adequately in the post, but if not here is a brief rundown of what exactly happens.
1. Whenever a Shadow appears, it creates a sort of mirror dimension where it is able to exist without regular people knowing. However, if it gets too close to a Human it is able to start bringing said human into the dimension. While each Shadow creates their own similar environment, when a lot appear at once the environments tend to meld together and can even encompass the whole city. It goes without saying that stronger Shadows can creates larger fields, Familiars creating the biggest. I haven't yet thought of a name of this phenomena, so if you guys have any suggestions please let me know! (I was planning on being Persona 3 trash and calling it the Dark Hour but that doesn't really seem to fit since this can also occur during the day, but is rarer and usually more contained. You'll only ever usually see a city wide dimension during night time).
2. Princes and Witches are able to tell when these dimensions have been opened nearby, but can only access them when transformed. Prince's like Kim who have abilities that give them enhanced perception of Shadows have the power to detect when one of these dimensions has been opened over great distances. Kim's still not at full power, but he is able to detect when one has opened anywhere in a 10 kilometer radius.
3. Regular people cannot perceive or sense what happens in this dimension, but events from inside that effect the physical world can still be sensed. Though the universe usually conveniently covers this up as a natural occurrence like an earthquake or thunder storm. That being said, they can still wander in if a Shadow gets too close to them and draws them in. They usually forget everything they saw upon exiting the dimension, if they are lucky enough to be able to.
3. Shadows are by nature really gross and disturbing, so get creative with the enemies you encounter. However they take a more generic form when travelling which makes them look less inconspicuous.
4. Characters who have yet to learn of their transformation, fear not you can still get involved in this. Your uncontrolled powers cause you to sometimes wander into these dimensions without knowing. Our characters can find you while in here, so try and organise that with another player.
If you have anymore questions regarding this unnamed phenomena then let me know.