Then He asked him, “What is your name?”
And he answered, saying, “My name is Legion; for we are many.” Mark 5:9
Satan has at his disposal a third of the heavenly host that followed in rebellion. (Rev 12:3, 4)
Demons plague us with different sinful addictions. Their abilities seem to be possession and oppression.
Demons seem invisible. I believe they exist outside the range of human vision, just as there are limits to our range of hearing.
In reading the Bible you discover demons can talk and physically afflict us.
Jesus believed and dealt with both the devil (Matt 4:1-11) and demons (Matt 4:24).
The disciples found out they had power over demons in Jesus name. (Luke 10:17-20)
Much depends on the Christian when it comes to demon possession.
Much also depends on the possessed person.
Luke 11:24-26 – “When an unclean spirit goes out of a man, he goes through dry places, seeking rest; and finding none, he says, ‘I will return to my house from which I came.’ And when he comes, he finds it swept and put in order. Then he goes and takes with him seven other spirits more wicked than himself, and they enter and dwell there; and the last state of that man is worse than the first.”
When a demonic spirit leaves someone, that person must fill the void with Christ.
Your body must become the temple of the Holy Spirit.