The sliding scale of muggle involvement measures how much impact ordinary people have on the plot of an urban fantasy story.
The lowest level of muggle involvement is when there are no muggles in an important role at all, or just one or two token muggles. Instead, every character with a large impact upon the plot is part of the supernatural underworld. However, more important muggles may show up in the first few chapters before the protagonist's Call to Adventure.
The middle ground for muggle involvement is when the plot is clearly about the supernatural but muggles and muggle institutions clearly impact the plot. The police might be unaware of magic and thus be unable to solve the murder of a high-profile wizard, but their investigation still has an important effect on the plot. An attempt to gather a set of McGuffins might be hindered by the fact that several have already found their way into museums or private collections.
At the high level, muggles drive the plot. They frequently cause plot-significant events for reasons entirely unrelated to the supernatural, and even supernatural beings spend a lot of time worrying about purely mundane things.
For the purposes of this trope, Occult Detectives, Monster Hunters and other characters who have no supernatural abilities but are considered unusual because they have seen through The Masquerade are considered to be honorary supernaturals.
- Dragon Ball and later Z had this happen in conjunction with Can't Catch Up. By the later arcs of Z, your impact to the plot became radically lower if you weren't: an alien, part alien, a god, an alien god, or a robot.
- Ghostbusters (1984) features high muggle involvement. While the Ghostbusters themselves are defined by their interest in the paranormal the majority of characters are regular humans and an investigation of the firehouse by the U.S. Environmental Protection Agency is a major plot event.
- Transformers has the human military actively taking part in taking down Decepticons.
- Lost Girl - Bo's sidekick, Kenzi, is the only human with a real impact on the plot.
- On Buffy the Vampire Slayer and Angel, we have the middle ground. While the main characters all have supernatural knowledge, they often have to deal with people who are oblivious. Often they are obstructive, but sometimes the characters gain key information from them, despite the muggles not knowing what the information is actually about. Note also though that a lot of episodes do not feature muggles at all.
- In Rivers of London the protagonists are all police-employed magicians investigating supernatural crimes but the cast consists of many ordinary people such as police officers, jazz musicians or Peter's family. When they are aware of the supernatural it is never portrayed as character defining trait, or rarely a trait at all.
- The Dresden Files varies by book but has at times gone entire books without including a single character not in the know.
- Jonathan Strange & Mr Norrell is firmly rooted in muggledom. The first two books revolves around the magicians interaction with high society and the Napoleonic War. Even when the plot shifts to focus on Strange's conflict with The Gentleman With Thistledown Hair the vast majority of characters are still ordinary people.
- Paul Cornell's novel London Falling manages to include a high level of muggle involvement in a world with a strong Extra-Strength Masquerade. While the villain is a witch and the protagonists possess The Sight the vast majority of the characters are regular people. The protagonists job as police officers is given as much importance as their modest supernatural abilities and their motivation is simply to arrest a criminal, supernatural or not.
- The Harry Potter series has very low muggle involvement, with the only ones regularly appearing are Harry's Uncle, Aunt, and Cousin.
- Ugly Americans has high muggle involvement. Zombies, wizards, demons and such are treated as ethnic minorities, and the main characters work for an agency charged with integrating them into mainstream society.
- W.I.T.C.H. has little muggle involvement in the first season, at least from Earth's muggles. In the second season we start to see a lot more plots and plot complications started by the Guardian's muggle friends, family and teachers.
- Steven Universe has most of its important characters as Gems, and after season 2 the majority of screentime is shifted to the increasingly complex backstory with Homeworld society, in contrast with season 1 which tended to split the difference between Beach City humans and the Crystal Gems. Even so, there's still the occasional episode that focuses on the side cast, and whenever something threatens Earth, the safety of Beach City's characters comes first.