b) always! no spell needed!
Pg 70 references "most supernatural creatures" without clarifying which. This is of course a remnant from when the power was originally written for Beyond the Supernatural where many of the supernatural creatures in the book had See the Invisible as a power, so I had assumed it was kind of an opt-in process...
Pg 87 "Supernatural Senses" only appears to referecnce nightvision and sensing other nightbane, but nothing about seeing invisible stuff...
I feel compelled to confront my negative assumptions as of noticing that on page 75 of Between the Shadows under the Necrophim's "Astral Form" it pretty much repeats the Astral Projection disclaimer EXCEPT it says...
- most supernatural creatures (including Nightbane) can see them
The addition of this parenthesis... should it be intended only for Necrophim in Astral Form, or should we take that as some kind of retroactive affirmation that Nightbane are able to see all other astral projectors too?
Pg 78 also says for the Torturian "Nightbane, and most supernatural creatures"
Maybe just these two are exceptions due to being the type of evil guys Nightbane tend to be the bane of? Or should Nightbane also be freely able to see Milleks and Tarantuloids and your casually roaming lesser psychics or sorcerers as well?
Also who might the exceptions to "most" be for supernaturals who can't see Necrophim/Torturians?