this needs to be a thing. please translate into english

Or you know you could just use the rules out of the book.

"Possession: The creature has the ability to possess a corporal form that
is not its own and introduce itself into its body, subjugating the will of the
host. While it is found within it, it will be able to use its own abilities as well
as that of its host, although it would need to use the physical characteristics
of the body. Its ability to take damage while within a physical form, depends
on its nature. If we are dealing with a Being Between Worlds, there is the
possibility that a sharp strike in the place that it is located in can damage
it normally. If it is a Soul, it does not take damage under conventional
means, but the physical form that it possesses does. The attacks based on
energy will effect the spirit as well as the individual possessed, subtracting
individually the LP of each one. The essence attacks can be used against
both at the same time or just against one, if and when the person casting
it is aware of the situation. The possession is permanent, but the body has
the right to a new Resistance check every day that goes by, or on every
occasion in which an action is taken that is completely against its nature."

Which is an Added Mystical Effect on pg 289 of the core book.