For the longest time, Chica was the least utilized out of the original four. Freddy is The Leader and has his gold variant, Foxy has unique game mechanics throughout the series, and Bonnie is directly associated with the Big Bad. In contrast, Chica is just... there, and is rarely given as much focus. However, later installments have given Chica more attention in an attempt to rectify this: in particular, the child possessing Chica has been given some extra characterization, as she was a little girl named Susie who was lured to her death by Afton promising to let her see her recently deceased puppy again. She also has A Day in the Limelight in Five Nights at Freddy's: Fazbear Frights story "Coming Home", and a voice line in Ultimate Custom Nightreveals that Susie was the first of the Missing Children to die.Security Breach also only has Chica and Freddy return as members of the Glamrock Band, with Bonnie's and Foxy's spots taken by Monty and Roxanne respectively.
While you're free to play as any animatronic (and then some!), some may be disappointed that they don't have any real dialogue or personality in cutscenes, excluding Fredbear, who acts as Mr. Exposition half the time anyway.
This is even worse gameplay-wise; the early characters get outclassed by later ones with better moves and stats. You want to play as Freddy for the rest of the adventure, for instance? You'll have a hard time using him later down the line then! It's even more apparent with the new area in Update 2, in which the enemies are so strong and your health is drained so rapidly you need the newer characters just to get through, and the Rainbow herself is so blatantly broken as a boss that you need these characters to even stand a chance.
Ballora. She's the only adult humanoid animatronic, and the only blind one, who is made to dance like a ballerina and to distract parents so that Afton can take their children. Also, if you believe Ennard, Ballora was against the plan to scoop you, not because of the obvious problems, but because she is afraid. With all of this depth, and especially knowing that she has a voice actress like Baby, you'd expect to get more from her than a Jump Scare, like her opinion on what's happening and such. Nope. After a harrowing Night Two endeavor where you have to crawl past her carefully, so that she doesn't hear you, Ballora gets scooped on Night Four, and becomes part of Ennard.
William Afton, the Big Bad of the franchise, is technically speaking the Big Bad, but is still largely Demoted to Extra, with most of the spotlight being given to his daughter, who was introduced just one game beforehand. Even in death, he doesn't get any last words, and is barely mentioned in the ending besides one scene.
At the end of Sister Location, Michael Afton was teased to become the new protagonist with a major story arc where he tries to find his father. While he is heavily implied to be the Player Character here, he still doesn't get to utter even a single line, and is reduced to a blank slate with his monologue about wanting to find his father being completely forgotten.
The other Glamrock animatronics get hints of Hidden Depths that aren't explored much: Roxanne is a Narcissist with an Inferiority Superiority Complex, Monty has a Hair-Trigger Temper, and Chica is not just a Big Eater, but experiencing the robotic equivalent of an eating disorder. Glamrock Freddy frequently alludes to them actually being as nice as him and that something must be seriously wrong for them to be acting as violently and erratically as they are. Add to that the interesting hints at their aforementioned Hidden Depths and the fact that they do genuinely seem to care about Freddy, and you have all the pieces for a potentially great character arc. Instead, the Glamrocks remain Brainwashed and Crazy for the entire game, with the player getting no option to get to know them beyond that. Some fans wish there was an option to free them rather than destroy them to use their parts to upgrade Freddy, perhaps even as its own ending.
Some people feel Vanny is criminally underused in proper gameplay, despite being the primary antagonist and receiving top billing. To explain, she is the first direct human threat, with an inherently disturbing concept and explanationbehindit. The Five Nights at Freddy's AR: Special Delivery emails do a good job illustrating her deteriorating mental state. Combined with a legitimately creepy design and notable Faux Affably Evil behavior, she became a quick fan favorite before release. Despite all this, she doesn't make as many direct appearances in actual gameplay as you'd expect, and is seemingly absent from the apparent true ending, despite being Glitchtrap's servant (she's accounted for in other endings, where she either dies, is expressly still active, or freed from Glitchtrap's influence). Word of God says there originally was a "Vanny Meter" game mechanic planned in which lingering in one area for too long would have eventually spawned her, but this was scrapped in development for running contrary to the game's exploration theme.
Gregory, despite being the protagonist, has had some people wishing he'd get a bit more development. Besides his desire to survive, his eventual bond with Freddy, and his snarkier moments, he remains pretty much a blank slate throughout the game, not really growing or changing at all. Heck, the game itself frequently hints that there is more to Gregory than meets the eye, given the repeated mention of his missing personal records and the question as to how he got into the Pizzaplex in the first place without a guest profile. Also, the one-star ending hints at Gregory possibly being a Homeless Hero, which adds an extra layer to the game's story. The Tales from the Pizzaplex story 'GGY' also adds a tantalizing possibility that Gregory is not only Ambiguously Evil but Patient 46, as Tony's friend 'Dr. Rabbit' may or may not be game!Gregory hacking animatronics and killing the school's counselors under the influence of Glitchtrap, which adds another interesting layer to the game's events. But none of these plot points are ever followed up on, leaving Gregory as a rather run-of-the-mill Protagonist Without a Past.
Luis Cabrera from the Special Delivery emails was commonly predicted to make a cameo in Security Breach, if not playing an important role. The emails establish him as a fellow employee of Vanessa's who is investigating her search history and is implied to be one of the few people who will acknowledge her Sanity Slippage. He also has some story significance by being used as an Unwitting Pawndue to his feelings for her. Luis is also given much more characterization than you'd expect out of a Small Role, Big Impact character: aside from being a Dogged Nice Guy, he oversteps boundaries not out of maliciousness but of poor social skills, he has serious self-esteem issues, and he even has a canon birthday and preferred cake flavornote he turns 24 in March and likes chocolate. In Security Breach, he's only mentioned vaguely in the Retro CDs, where Vanessa briefly talks about him on two separate occasions, and later the subject of her odd search history is brought up.
Of all characters, William Afton himself is perceived by some as being underutilized in this game. He only directly appears in the True Ending, in which he isn't fought directly and instead uses the other animatronics, including Freddy, to fight Gregory, and his involvement ends with the Blob dragging him offscreen in another fire. However, the reveal that he's being resurrected under the Pizzaplex, while it did receive Foreshadowing, could have held larger narrative weight in other routes, especially considering he is now a Technopath, and was previously established to be capable of Grand Theft Me and brainwashing as Glitchtrap.
Sammy. Much of Charlie's trauma revolved around losing him, and in The Twisted Ones, she claimed to feel his presence. Despite the confirmation that William killed Charlie and Sammy is likely still alive, he doesn't appear on-page.
Charlie herself. All of her character development is abandoned the moment she finds out that she's actually a robot created by her father, and essentially just becomes a Living Prop in her own story while Carlton takes over as the main hero.
