The Authors 3 Forum Catagorizing

An Anti-Villain is the opposite of an Anti-Hero; while the anti-hero often fights on the side of good, but with selfish motives; the anti-villain plays a villain's game, but for a noble cause... at least in their eyes. They may be more noble or heroic than an anti-hero, but the means to achieve their ends are often considered exploitative, immoral, unjust, or just evil.

Sometimes, they may simply be a villain with gentlemanly qualities or with some sense of justice. Anti-villains will occasionally side with their rivals (usually the protagonist) if a greater threat than themselves comes or it's in both of their best interests. Often times, if they do join the protagonists, they are distrusted, but can get along and eventually redeem themselves.