Metaphysical

A dynamic place of consciousness and ideas. You can enter someone else's mind but you can only see what they’ll show you. It manifests itself for different people.

Books, being ideas put the the page, are quite painful to the astral traveler if flung at them.
Therefore, theoretically pages can be used as projectiles in this plane. Ghosts exists on this plane. It's the 3rd closest to the Material Plane. Time is slowed by an eighth. So 2 Material Plane seconds equals 16 Astral Plan Seconds.

Any language just as the Material World.

The geography manifests itself for different people. For Bee, everything is simple bright flat colours, very shape heavy.
The landscape is based on the surrounding people's state of mind at the time. The astral plane feels like an m83 song visualized.

Rarely has any activity. Since it is mind-based, temperature is an illusion.

Since consciousness can be detached & float aimlessly, some entities can possess others.
It is quite hard to do so as one can only enter the MINDSCAPE with consent. After doing so, the intruder would have to identify the host's 'Inner Spark'. A fundamental truth or building block on which every other aspect the host is centered around.

The psychic parasite could then infect, corrupt, gain control and, in the case of powerful Aemara can physically alter the host in the Material Plane. To the outside world, it appears as a 'possession'.

Sadly those facing mental issues can sometimes fall prey easily to these horrors, though not by any moral or personal failing. The added stress and savvy of a particularly tricky parasite/intruder can best the most fortified minds. The intruders have been known to ruse their unsuspecting hosts through the illusion of cures or perceived salvation of their affliction or condition.

All these circumstances often lead to tragedy. Though some hosts can and have fought back intrusions with the help of accomplished magicians and healers.