In the Great Tribulation, right before the second coming of the Lord Jesus Christ. Satan (the dragon), the antichrist (the beast), and the false prophet will dispatch demons to deceive the nations to fight against Him and His army.
Cain was under extreme demonic oppression for a while before he lost his relationship with the true Living God, which is Satan’s goal for all God-fearing believers in Jesus Christ.
The serpent or Satan the devil, murdered Adam and Eve in the very beginning by making them stumble through deception. He killed their relationship with God.