Not all characters in the series manage to share the spotlight with the main cast. Here are the following characters that were unfortunately not given their deserved screen time:
- Toad and Bowser are particularly striking examples. After both were core members of the cast since the beginning of the series, with plenty of personality and established roles as mainliners, they started diminishing heavily in appearances during 2019 and were effectively reduced to cameos by 2020.
- Desti is one of the biggest modern examples. First appearing in "If Mario Was In Splatoon 2", she became fairly popular despite disappearing after that episode, and many fans wanted to see her again. Her return for the Anime arc and subsequent development only gave her more fans, and the fanbase outright took for granted that the arc would end with her and Meggy finally becoming friends, or at the very least developing a friendlier rivalry. Instead, Desti unexpectedly became SMG4's first permanent Character Death, a decision many believe ultimately did more harm than good in the long run for how it wasted her and for the divisive precedent it set.
- Jeeves. His intolerance of Mario's idiocy provides the perfect foil to him, especially considering nowadays most of the modern cast is friends with Mario, Peach, and Toad are Out of Focus, and SMG4 was flanderized into being "the meme guy" rather than Mario's foil. Jeeves would be the perfect modern foil for Mario. Unfortunately, Jeeves started dropping off in appearances heavily during 2019, and was relegated to cameo status after “Super Mario Taxi”.
- The Anti-Cast, barring Melony, are notorious for getting cast aside after the YouTube arc, doubly so considering all of them except Weegee Doll are OCs. Many will admit that they have good concepts, but rarely getting any attention prevents them from capitalizing on it. SMG4 seems to have at least recognized this, as the trio of Belle, Whimpu, and Rob have been collectively referred to In-Universe as "the side characters" at times.
- Anti-Shroomy seemed to be getting built up as a major recurring villain and a big player of the YouTube arc. Unfortunately, he ended up barely being used for anything and stopped appearing altogether after "Mario and the VILLAGE".
- Melony herself started getting this post-Revelations Arc, falling hard into the background after having a fair amount of relevance since "Mario's Mask of Madness". Many of the appearances she does make have no mention of her finishing Axol's manga or her potential rap career with Bob and tend to not have her do much despite her wanting to protect her friends. Many attribute this to her becoming too powerful to be properly used without breaking the plot wide open, not having any solid dynamics with the rest of her friends outside of Bob, and the fact that she lost Axol, the one character she was able to bounce off of before.
- Part of why Axol is a Base-Breaking Character is because of this. He had a great design and was touted as a famous and powerful character with a unique concept that was perfectly fitting for the Anime Arc. Yet after the arc concluded, it seemed as if SMG4 and the writing team had specifically created him for that arc and had no idea what to do with him once it finished. Post-Anime Arc, he sporadically appeared and the few times he did were at his expense rather than him doing anything related to the plot. While other original characters raise the criticism of "why are they given so much screentime for doing so little", Axol is probably the only original character to raise the question of "why push aside the one character that had a unique concept?" Making it worse was that when he was brought back, he was promptly "flanderized", leading to calls of his character being butchered and that Axol, as the eccentric manga artist, was now wasted for an entirely different reason. His death at the end of the Genesis Arc was the final kick in the teeth, as plenty of fans had gotten used to the side of him that crushed on Melony and were looking forward to the adventures they would've had together—not long after his pen finally got fixed, no less.
- Sam and Kenji, Meggy's former Splatsquad teammates, all but vanish after their debut alongside Meggy. Meggy's Destiny only gives them a few seconds of screen time in a flashback scene at the beginning. Many pointed out that they could've been members of Team Killer Ink, wanting to prevent Meggy from winning Splatfest out of revenge for her Drill Sergeant Nasty behavior possibly driving them away and explaining their absence. It could've both made the movie more emotional and given Team Killer Ink a better motivation for being antagonistic towards the main cast, preventing them from just being inferior Desti copies.
- There are plenty of people who wished Niles was an actual student at Omnia Academy and not Zero messing with Melony's head.
- The real SMG0 finally makes his debut in the Revelations movie, with him being shown as a Nice Guy with tons of lore and backstory potential as the first SMG. He's Killed Off for Real at the end of the movie after only showing up a third of the way through.
- Two characters that were prominently shown in episodes building up to the Puzzlevision saga ended up not being used in it.
- Clench comes to life just in time for the events of the Puzzlevision Originals to get started, making viewers think he's going to play an important part later, either as a hero or an affiliate to Mr. Puzzles. He ended up not doing anything at all. In fact, once he shuts off before the SMG4 crew stumbles into the basement, he doesn't come back online for the rest of the saga.
- At the beginning of "No TV Make Mario No Okie-Dokie", Depresso is seen rushing to the SMG4 castle in the rain, only to get struck by lightning. This, combined with the fact that Mr. Puzzles makes his move in the castle's basement, where Depresso lives, made some viewers think the clown had some role in Mr. Puzzles' plan, and that he was trying to warn the SMG4 crew. This ended up being the last we see of him for the rest of the saga.
