The great dragon was hurled down—that ancient serpent called the devil or Satan, who leads the whole world astray. He was hurled to the earth, and his angels with him.
~ Revelation 12:9

How you have fallen from heaven, O morning star, son of the dawn! You have been cast down to the earth, you who once laid low the nations! You said in your heart, 'I will ascent to heaven; I will raise my throne above the stars of God; I will sit enthroned on the mount of assembly, on the utmost heights of the sacred mountain. I will ascend above the tops of the clouds; I will make myself like the Most High.'
~ Isaiah 14:12-14

For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms. ~ Ephesians 6:12

Demons can:
cause lunacy ~ Matthew 4:23,241; 7:14-21; Mark 5:1-8; 9:20
cause mania ~ Matthew 4:23,241; 7:14-21; Mark 5:1-8; 9:20
cause suicide ~ Matthew 4:23,241; 7:14-21; Mark 5:1-8; 9:20
distribute uncleanness ~ Luke 4:36
create lust ~ John 8:44; Ephesians 2:1-3; I John 2:15-17
and manifest supernatural strength ~ Mark 5:2-16

The people were all so amazed that they asked each other, 'What is this? A new teaching—and with authority! He even gives orders to evil spirits and they obey Him.
~ Mark 1:27

And Jesus rebuked him, saying, Hold thy peace, and come out of him. And when the devil had thrown him in the midst, he came out of him, and hurt him not. And they were all amazed, and spake among themselves, saying, What a word is this! for with authority and power he commandeth the unclean spirits, and they come out.
~ Luke 4:35-36

Then he called his twelve disciples together, and gave them power and authority over all devils, and to cure diseases.
~ Luke 9:1

He that heareth you heareth me; and he that despiseth you despiseth me; and he that despiseth me despiseth him that sent me. And the seventy returned again with joy, saying, Lord, even the devils are subject unto us through thy name. And he said unto them, I beheld Satan as lightning fall from heaven. Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you. Notwithstanding in this rejoice not, that the spirits are subject unto you; but rather rejoice, because your names are written in heaven. In that hour Jesus rejoiced in spirit, and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes: even so, Father; for so it seemed good in thy sight. All things are delivered to me of my Father: and no man knoweth who the Son is, but the Father; and who the Father is, but the Son, and he to whom the Son will reveal him. And he turned him unto his disciples, and said privately, Blessed are the eyes which see the things that ye see: For I tell you, that many prophets and kings have desired to see those things which ye see, and have not seen them; and to hear those things which ye hear, and have not heard them.
~ Luke 10:16-24

Then He will say to those on his left, 'Depart from Me, you who are cursed, into the eternal fire prepared for the devil and his angels.'
~ Matthew 25:4

Be of Sober Spirit, be on the alert. Your adversary, the devil, prowls about like a roaring lion, seeking someone to devour.
~ I Peter 5:8

Submit yourselves, then, to God. Resist the devil, and he will flee from you. ~ James 4:7

Our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms. ~ Ephesians 6:12