Ethics is a field of philosophy, which studies moral values and systems of values, into which they unite. The task of ethics is to define which is right and which is wrong in terms of behavior and thinking. The good and the evil are important categories of ethics, which are believed to be absolute. Yet, relative ethics suggests that these categories can vary depending on a person or a group of people. Both approaches can be used depending on the situation, yet there are ethical theories that belong to either group.
Speaking more about absolute and relative ethics, it is worth saying that absolute ethics suggests that the moral principles are universal and can be applied everywhere regardless of the situation, place, time, ethnicity, etc. For example, Kant’s theory of universal laws, says that there are ideas about the good and the evil, which should not be verified in practice because they are inborn and are known without verification. This also gives an idea that motivation is more important than outcome, because good intentions can have negative consequence and vice versa. Another example of absolute ethics theories is the theory of Natural Law, which focuses on proper conduct as human duty.
In contrast, relative morality exists when it its estimation depends on a particular situation. For example, to lie is wrong but sometimes lying out of mercy can be ethical. Absolutists would say categorically that abortion is wrong, while relativist would justify abortion in some particular cases, like for instance becoming pregnant as a result of abuse.
In this context, Satan does not have ethics, if we speak about absolute ethics, and he might have his special ethics, which is different, if we speak from relativism perspective. In terms of absolutism, Satan is evil not because of his actions but because of his motives. In fact, his evil intentions can have positive consequences.