"Sometimes a guy needs a pal out of the locker room."
—Cooper Manning, on his friendship with Saints QB Drew Brees
Part of the storytelling method is to make a character relatable to the audience. The audience would like to be relatable to the hero because who doesn't want Phenomenal Cosmic Powers and to get the girl (or guy)?
But since we're mundanes, the Muggle Best Friend is our relatable character—an ordinary person drawn into the hero's extraordinary world.
They have no super powers, no magic, no Applied Phlebotinum. But despite the danger, they're loyal and will stick to the side of their heroic best friend no matter what the Call to Adventure may throw in the hero's path. They are frequently Secret Keepers and can be plucky Comic Relief as well.
They represent the tie that the character still has to their original, pre-super life. They will usually interact with the main character's family, friends and Love Interest even when the hero is unable to. They are most common in shows where The Hero does not have a Five-Man Band - if they do they will be overshadowed as the position of Best Friend tends to go to The Lancer, but might still serve a background function. At some point they will be held hostage by the villain and they are often in the risk of getting Killed Off for Real to provide The Hero with a reason for revenge.
Note that the key trait of the character is that they are a piece of the character's former life and so they do not exclusively appear supporting superheroes or magical beings, but simply shows when the hero moves into a different league after receiving the Call to Adventure.
Also, Love Interests can also be Muggle Best Friends, and will provide a good reason to be equally worried about your secret life and your normal life, especially if you are on a Wake Up, Go to School, Save the World schedule. The Chick can also double as Muggle Best Friend. In circumstances like these, an Understanding Boyfriend may come into play.
Occasionally you will have the Muggle Best Friend wish for powers so they aren't always a liability or potential hostage; they usually end up with powers that last for one episode only—just so they realize being normal is cool enough on its own, or that having powers isn't as cool as it's cracked up to be. For flavor, fits of jealousy brought on by I Just Want to Be Special may pop up and strain things between them before The Power of Friendship reasserts. Once in a while, the friend will leave the trope when they acquire some sort of metahuman abilities.
May cross over and into Badass Normal territory, but mainly Muggle Best Friends are just ordinary people. Related to A Boy And His X, obviously. Especially when the X is super powered. More than one may team up to become Those Two Guys. Compare Fantastically Indifferent.
- Naru from Sailor Moon.
- Cardcaptor Sakura has Tomoyo.
- Gunslinger Girl has Claes.
- Magical Girl Lyrical Nanoha has Alisa and Suzuka. Eventually phased out come the third season and beyond, when The Hero decided to move out of earth.
- Puella Magi Madoka Magica has surprisingly, the titular character Madoka herself. The series is a tug of war between QB (for) and Homura (against) over whether she turns magical girl.
- Episode 10 reveals that in the original timeline, Homura was the Muggle Best Friend to Madoka.
- Played straight with Hitomi, who serves as Madoka and Sayaka's friends. It's soon played straighter than most Magical Girl shows would usually go and have her be one of the straws that break Sayaka's back and drive her to despair.
- Mai of My-HiME has Chie and Aoi, two girls who are never aware of or involved in the Himes' conflicts.
- In Bleach, Mizuiro, Keigo and Tatsuki.
- Superman's pal Jimmy Olsen; subverted when he takes on the mantle of Elastic Lad or any one of the other hundred or so super-identities he's temporarily had over the years.
- April from Teenage Mutant Ninja Turtles is a good example, and this is true of the Animated Series as well.
- Paco and Brenda to the third Blue Beetle, Jaime Reyes.
- Doiby Dickles to the original Green Lantern, Alan Scott.
- And Thomas Kalmaku (formerly known as Pieface) to Hal Jordan.
- At the beginning, Harry Osborn was this to Spider-Man.
- James Rhodes to Ultimate Iron Man. This version of Iron Man is a mutant of sorts.
- Bucky Barnes and Captain America (comics), back during the war.
- Woozy Winks to Plastic Man.
- In Star Wars we have Han Solo to Luke Skywalker.
- Cherise is the Muggle Best Friend to Joanna Baldwin in the Weather Wardens series as of Windfall, and the Love Interest of Kevin as of Thin Air.
- Laura is the Muggle Best Friend to Kate in the Adventures of a Demon Hunting Soccer Mom series, and she's the self-titled Sidekick as well. Even after reading the first book, it's clear that Kate's daughter Mindy will be the Muggle Best Friend to Kate's daughter Allie when Allie ends up trained to follow in Mom's footsteps.
- Dillard from Kingdom Keepers, though unlike most examples he's largely left out of the loop.
- Bella's friends Angela, Jessica, Mike, Eric, Ben (Angela's boyfriend), and Katie (Eric's girlfriend) in Twilight. The last two are cut from the films. Angela is the one Bella is closest to
- Clary's friend Simon in the Mortal Instruments series.
- On Wizards of Waverly Place: Harper to Alex. Zeke to Justin. Theresa to Jerry.
- Chloe to Clark on Smallville (Until she develops her own powers). Before Chloe, it was Pete Ross.
- The Scooby Gang in Buffy (until Willow develops magic powers of her own). Xander retains this role all the way through the televised run of the series even as other characters grow beyond it.
- Virtually every companion ever on Doctor Who, with the exceptions of fellow Time Lord Romana, half- Time Lord River Song, time-traveling immortal Jack Harkness and girl with a crack in time inside her head Amy Pond. Most of them are young (the exceptions being Adelaide, Donna and Donna's grandpa Wilfred) and human or humanoid, with no special powers. Even the aliens (Adric, Nyssa, Turlough) are fairly normal - they might be smart, but nothing beyond a Brainy Brunette or The Smart Guy.
- Ando on Heroes... until he got powers of his own. (Sensing a pattern here?).
- Claire had Zach who had no powers, and later, Gretchen before their Relationship Upgrade
- Peter has Hesam
- And lastly Noah Bennet could've been The Haitian's powerless pal.
- Partial example: Teen Genius Doogie Howser's best friend Vinnie, a guy of average intelligence that helps him relate to the world of normal teenagers.
- Partial example: Nathan from Queer as Folk hangs out with his straight female best friend from school. She's pretty much the only straight person on the show.
- George and Katie from No Ordinary Family. (Until she got a super powered baby who sometimes lets her use the powers, and he got put on the 'Super Powered Crash Test' plane in the last episode.)
- Maria Deluca from Roswell. Also Liz and Kyle until they began to develop powers of their own.
- Keely Teslow to Phil on Phil of the Future, though she quickly became the Love Interest as well.
- On Grimm, both Hank and Juliette can be this to Nick.
- Static Shock had Richie, Virgil's best friend—but it became subverted when in the third season they upgraded Richie to Bang Baby as well.
- Spud and Trixie to Jake from American Dragon: Jake Long. Spud had his A Day in the Limelight episode as a frog boy.
- Tucker and Sam to Danny on Danny Phantom. Tucker got ghost powers for one episode. Sam got plant powers for one episode.
- Frida to El Tigre. She actually stole the El Tigre belt to go out as La Tigresa to satisfy her wish to be special too.
- Brad and Tucker to XJ-9
- Rainbow Brite had a boy from Earth that she was friends with.
- Most of the human friends in various Transformers media.
- Subverted in Transformers Animated, Sari appears to be this. She is, in fact, a cybertronian protoform in a human alt-form.
- So far, Noah from Generator Rex is this to the titular Evo.
- Gwen from series 1 Ben 10 until she got her Lucky Girl powers and then began studying magic.