Are the apparitions humanoid/how big are they?
The apparitions vary in size and form, but between apparitions and over time. They can be as small as a lapdog or large as an elephant depending on their own natural energy levels. They take a variety of forms, including looking rather formless, but all forms lack any particular detail that would identify them to a human eye (such as well-defined facial structure, etc). They can tell each other apart based on other traits, including their energy signatures, but us poor humans aren't so lucky.

If they are immune to physical injury, how do they react to extremely cold temperatures?
Cold would slow them down, but not stop them. The lower the temperature, the more that they appear to be molasses in January.

Are they capable of turning incorporeal?
Yes! To an extent. Any material that conducts electricity is essentially a conduit for the creatures and they can travel along quite merrily, passing through that material. If said material passes through a wall (like a wire), they could theoretically pass through it as well by travelling in the wire.

Are you now re-reading all these questions in Shiro Shinobi’s voice?
Yes! No! ...I don't know?