Knights of Cerebus

In order to add more drama to a series which has been, up until that moment, lighthearted and comedic in nature, a villain (or antagonist of some sort) is introduced and is portrayed as a genuine threat, in contrast to the bumbling and comedic villainsthe heroes have faced before.

This villain's arrival is usually heralded by a sudden downturn in humor, to show the audience this guy means business. In other words, a catalyst for a drastic change in mood toward the dark and dramatic.There are examples of characters who take the story to darker territory without being villainous in the slightest, but this trope is reserved for evil creatures.

In shows that are generally Lighter and Softer, said villain may have some light-hearted or comical traits, but still gives a much higher sense of dread and genuine threat to the heroes than previous adversaries. Some cases of the trope may be harder to define by comparison in a particularly ineffective Rogues Gallery, though a clear cut example at the very least can actually place the protagonist in real danger compared with the Harmless Villain that poked his poodle in a previous arc. A typical symptom of Cerebus Syndrome.

A Knight of Cerebus is very likely to be an assassin trained for killing, or even a blatant Hero Killer who posed actual threat, but also runs the risk of becoming a Villain Sue. Arguably a subtrope of Threshold Guardians. See also Dead Serious, Not-So-Harmless Villain. The show may Shoo Out the Clowns first. Often, this results in a case of Vile Villain, Saccharine Show. When this kicks off Cerebus Syndrome, his or her arrival is a Gut Punch. Sometimes, this type of character, if bad enough, can be a Complete Monster if they have no redeeming traits and do terrible things by the standards of history in an initially more lighthearted series.