A lot of fan speculation has served them well in most modern-era SMG4 arc videos. Here are the following instances:
- Many people accurately predicted how the Waluigi Arc would end. Since Wario made a promise to bring Waluigi home and treat him better in "Mario The Scam Artist", and acceptance was Waluigi's Logical Weakness, it was impossible not to assume that Wario would eventually talk Waluigi down by openly accepting him. Sure enough, that's exactly what happens, albeit with a little effort.
- After SMG3 was revealed to have a PhD in therapy and had gotten his talk show a la Dr. Phil, many were convinced it wouldn't last, and that SMG3, one of the show's earliest and most recurring antagonists, mind you, would slip back into his villainous ways. Sure enough, "A Day in the Life of Everyone" marks his show's cancellation, and in the "Where Are They Now?" Epilogue, he is shown brainstorming on evil plans and ways to get back at SMG4 once more.
- While not everyone figured it out, a good majority of people guessed that Francis was behind Meggy's kidnapping since he was around to see how Ink Weaver was powered up through Inkling Ink and his continued fawning over Ink Weaver in "Mario Saves Anime".
- A few aspects of SMG4's fourth story arc were guessed ahead of time:
- That the arc would center around YouTube since the site and Susan had become a common theme of the early episodes of the arc before they were known to be part of the arc.
- That SMG3 would be the Big Bad due to "Mario's Spicy Day" implying he would return for revenge, Word of God confirming SMG3 would have a bigger role, and him getting a voice actor, which is usually a sign of a character getting an important role.
- SMG3's master plan (which is to replace the main cast with his cast) due to the WOTFI 2020 trailer outright showcasing this.
- Meggy getting a permanent English voice due to "Mario Gets【Ｗｏｋｅ】" showcasing Lizzie's voice for Meggy when her voice got temporarily changed to English by The YouTube Remote.
- Meggy's departure. With WOTFI 2020 giving her a professional VA, many fans started speculating that she was getting her own series, citing the many changes made to her character over the years to make her a full OC. When said series was teased in the GLITCH channel's introduction video and hints of it started appearing within SMG4, many believed it was only a matter of time before she left for Port Aurora in-series. "The Pursuit of Happiness" has her get a ticket to Port Aurora from her friends, with a special video showing her departure.
- Before the release of the 10 Year Anniversary special, a post on the subreddit questioned why the two then-unnamed hobos were featured in the poster despite being minor characters. In the comments, a user known as Chardoggy1 predicted the possibility that they were SMG1 and SMG2 given the numbers on their hats, and he couldn’t have been more right.
- The Genesis arc had quite a few big theories confirmed to the point that some joked that fan theories had to be a partial driving force of the arc:
- A long-running theory concerning Mario was that he never permanently dies because his life is tied to the SMG4 Universe and that if he dies, the universe goes with him. Mario being revealed as the Avatar of the SMG4 Universe and YouTuber Sunflower's video covering the "SMG4 Iceberg" gave this theory major traction until "The Other Universe" fully confirmed it, showing exactly what happens when a universe's Avatar is killed and cementing Mario's role as a Barrier Maiden.
- Some Genre Savvy fans deduced from Mario saying "yeah, no one died surprisingly" at the end of "Into the Dark Web" and from the subtle (at the time) increased focus on certain characters alone that Axol would die by the end of the arc. Some even further predicted it would be used as a catalyst to mature Melony.
- Many fans managed to piece together Zero's origin just from the flashbacks shown in the 10th anniversary and "The Other Universe"; that he was a former SMG with an Avatar of his own until his universe was destroyed.
- From the moment they appeared in "Mario Goes to College", the fanbase agreed the Box Club would be important based on the ominous speech the leader gave at the end of their debut episode, the leader having a voice actor and their box masks having custom GLITCH show-esque expressions, all staples of OC content and telltale signs that they would be important story-wise. Many further predicted that they were related to Zero, deduced from their club logo having a 0 at the center.
- Zero still being alive after the Genesis arc. Practically everyone doubted he was killed off for good at the end of WOTFI 2021 despite the crew and the main cast's claims In-Universe that he was destroyed. The numerous references to Zero, the seeming post-mortem buildup of his character, Luke confirming there was more to the story of Genesis, and James saying "Zero is not done yet" during a Deltarune stream left many outright taking his return for granted. This was before Niles' Zero-esque traits made the general fanbase gravitate toward him.
- Fans had a notoriously easy time dissecting Niles as a character to the point that nearly everything speculated about him turned out to be correct. Him being related to Zeronote and being in Melony's headnote was predicted months before "Absolute Betrayal" confirmed both.
- Regarding the God Box, plenty of people correctly guessed that it was connected with Zero in some way. To elaborate, it created Niles, who was merged with SMG0 to create Zero.
- Fans accurately predicted that the mysterious door in Saiko's house that kept being brought up as a recurring joke involved Kaizo, the main protagonist of the game she was pulled from, in some way.
- SMG4's temporary IP change design in "If Mario was in... Splatoon 3" was almost immediately taken as a soon-to-be-permanent redesign despite it being reversed by the end of the episode, with savvy fans citing that it had both a well-made GMOD model and a custom SM64 model with numerous custom expressions as evidence for this. The fact that a similar foreshadowing trick had already been used for Meggy's English voice change during the YouTube arc helped. A subset of people also predicted that SMG3 would change too so as not to break the lore of the Cosmology Saga, and that he would have a beard to look like his voice actor, James, in the same way SMG4 was changed to look like Luke.
- Following SMG4's plan to build a new castle at the Showgrounds, some fans have wondered if Depresso would show up there in some way, shape, or form. Sure enough, he appeared in "The Very Safe & Legal SMG4 Show" and subsequent episodes of living and/or rummaging in the property's dumpster.
- On June 14th 2023, SMG4 released this tweet
and asked "what Tari doin". Details were vague, but fans speculated that she's wishing upon a star for a redesign. Three days later, she would end up getting one. - Simply by the hints offered in the episodes preceding Western Spaghetti, fans were able to easily decipher that One Shot Wren would end up serving as the Arc Villain. Sure enough, the movie confirms this.
