demonic

If a being is demonic, it is a demon.

Example: They were trying to summon a demonic spirit.

If something is demonic, it comes from or has to do with a demon (or demons).

Example: The story was about someone who learned to cast demonic spells.

If you are demonic you have great energy and strength.

Example: The ancient Celts were said to be demonic in battle.

If you are demonic you are a very evil person.

Example: The crazed killer was completely demonic.