Dear Maria:

There are different levels of demonization. Depending on the author one can read about anywhere from three to seven. I identify seven different levels. The last level on everyone's list is that of possession.

I have no idea where this priest comes up with the idea of "temporary possession" as opposed to any other kind.  All possession is temporary, at least for those who die in a State of Grace. Even if the person is not freed in this life, at death, that possession no longer exists assuming the person dies in a state of grace. People who are possessed are not automatically damned. They can be in a State of Grace like anyone else and go to heaven. No one takes a demon with them to purgatory and heaven

In terms of possession itself, a possessed person can certainly have varying levels of intensity depending on which demons have possessed them (some are more vicious than others or more difficult than others.).

The most difficult kind of possession is what is sometimes called "perfect possession" (which is really an improper terms in my view) On this form, the possessed person has freely invited demons into himself and also cooperates, "with those demons with full consent of the mind and will, in the demon's desire to destroy God's Kingdom and children" [Fr. Thomas Euteneuer, Exorcism and the Church Militant (Front Royal, VA: Human Life International, 2010) 40]. It is certainly hard to believe someone might deliberately choose this, but we have had two or three clients who did just that, later regretting it, and coming to us for help.

God Bless,
Bro. Ignatius Mary