Flu shot (Image: Spencer Platt/Getty Images News/Getty Images) Misconceptions. Developing mild flu-like symptoms does imply the flu shot causes influenza. These side effects are brief and are due to the body's immune response. Some concern was raised about the potential link between flu shots containing the preservative Thimerosal and autism in recent years.
Definition: Oppression is a type of injustice. Oppression is the inequitable use of authority, law, or physical force to prevent others from being free or equal. The verb oppress can mean to keep someone down in a social sense, such as an authoritarian government might do in an oppressive society.
Because (in the usage you linked to) it refers to the 'bad guy' from a film or book. In the more general sense, it means opponent or adversary. The OP is asking specifically for a term describing someone who takes pleasure in causing pain and antagonist does not carry that connotation.