In certain religious contexts, evil has been described as a supernatural force

4.Can you be both good evil?
It is nearly impossible for any human to NOT be both good and evil, as the human destiny is one of redemption. Every human is somewhere on this journey, with the possible exception of narcissists, and some others with Cluster B personality disorders. People who believe they are already perfect, and do not reflect upon their inner selves. There have been, I believe, a few humans who reached perfection, while in this material plane.
While not wishing to push a specific religion, I offer the example of Jesus Christ as one who embodied spiritual perfection. If you look at the example of Christ, you see one who embodies no selfish motives. He does not seek to own anything or gather any riches. Nor does he seek to have power over anyone. He builds no organizations or power structures. He preaches a gospel of simplicity, humility, tolerance, forgiveness, peace, love for one's fellows, giving of all one has, including one's physical life, if called upon. He speaks of spiritual riches being where one' real treasure lies.
The above is one example taken from spiritual literature. The message of all great religions is the same. All real treasure is of a spiritual nature. The physical life and material things are ephemeral, not to be idolized. All characteristics of Being, in this way, are Good. All characteristics of Being the opposite of this way, are Evil. Good and Evil are direct opposites of Being. It is also true to say Good is Light, and Evil is the absence of Light. This is a light we bring to our consciousness, through our choice to bring awareness. In this way we grow in spiritual light, and redeem the places of darkness within us. This is the path of human redemption.We are all part good and part evil. Some among us have very little good, and some have very little evil. Most of us are somewhere in between.There is a use for evil, in the process of human redemption. Redemption is a process of suffering. Without suffering, no redemption. We cherish our egotistical and selfish natures. To understand how much, think of a narcissist who believes his ego trinkets are of far more value than treasures like love and empathy, and the soaring beauty of spiritual love--agape. He clings to his bits of tinsel, believing them to be chests of gold. On a lesser scale, every person suffers in relinquishing an ego trinket. A beautiful young woman suffers to have lost her beauty in an accident. She may gain in inner beauty. A brave young soldier suffers to have lost the power of his body in combat. He may gain in inner valor. A narcissist's victim loses in romantic love. She may gain in spiritual love. All of these gains come from ego losses. Notice I say "may gain." May or may not. It depends on our choices, which have to do with our courage to suffer (bend), and our willingness to suffer (accept and grow inner treasure). If we choose the path of lighting our consciousness, of grieving our losses, loosening our hands from them, and growing inner treasure, we choose the path of redeeming our inner darkness.As well, goodness shines a light on darkness (evil) which causes it to shrink away, and to lose its power and grip. That is part of what is happening with the questions and answers on Quora about narcissism. Light is the enemy of darkness. Truth is the enemy of Lies.