First, Jesus never made fun of evil spirits. He took it very seriously. Second, Always, look up in the Bible what people tell you. If it cannot be found in God's word then it is probably a lie.
Ghosts are what they call familiars. Demons take the form of a person or animal that has died to fool others and lead them away from knowing God. Ghosts are not the actual person who has died, but a trick. Demons can scare Christians but cannot possess them. A Christian can dabble with these things games etc. but the consequences can be serious. Jesus says to have nothing to do with them. God gives everyone free will. A Christian can turn away from God and accept the devil. The question is if a person is truly a Christian and accepts the devil, was he truly a Christian to begin with?
People who are possessed can have the demon casted out, only if that person wants to. After the demon is gone and they have accepted Christ they cannot be re-possessed. IF the person does not accept Christ into their hearts then they can be possessed again, but with even more demons. The Bible says that when a demon is casted out it will leave that person,
go through the desert (dry spells). It will later come back and if the house (the person) is empty (Christ is not living there) it will occupy the house again and bring with it other demons (multiple possessions).
Stay away from demonic games etc. by playing these you are opening a gateway into your soul and demons can influence people to do things.
As for your friend and her pastor. Tell her that a Christian should ask questions. That is how we learn and become stronger in our faith. It is the job of a pastor to take care of his flock (people). I believe that the problems Christians, especially teens, have today is due to the churches not addressing these issues. If her pastor had asked her to leave because of the questions, then she really should find another Bible-Based Church.