- Partially jossed with Sonic Chronicles and Sonic Generations, which either imply or outright state that the Classic and Adventure games are in the same general canon. Although this could be a red herring on the part of the storywriters.
- Specifically, the EVA units and E-100 Series both utilize the same tethered power supply and three-minute battery backup. Eggman's improved on the design by allowing the E-100 models to replenish their power supplies and even overcharge it by using the power supplies in his other creations. Gamma restoring its energy reserved by destroying Eggman's machines wasn't a mistake, its entire series was built from the ground up to do that.
- Big's initial cutscene shows him at his hut in the Mystic Ruins, which is practically right next to Lost World, and that temple is exactly the type of place you could imagine Froggy running off to. Also, after this cutscene, you find yourself in Station Square, not the Mystic Ruins where you'd expect, almost as if the developers cut out a section of the story there.
- What design feature do all of Big's levels have in common? Water, obviously. In fact, he goes to every Action Stage with water...except Lost World, that is.note Lost World has a room that's filled with water, and it's huge. Obvious place for Big to fish for Froggy.
- Have you ever noticed every Action Stage is visited by exactly three characters? Well, except for one that is. Which one? Yep, you guessed it.
This game introduces us to the E-100 series, who are all named after Greek letters. Only six appear in the game, Alpha to Zeta.
The Egg Keepers are confirmed to be E-100 robots, unfortunately, we don't know their numbers or names.
Considering there are only a small handful (this troper counted about 15 across all levels with every character), and they appear in only two levels, the Hot Shelter and the Final Egg, it's possible these were meant to be the remaining 18 robots, Eta to Omega.
Of course, Sonic Heroes introduced us to the actual E-123 Omega, and the IWD comics (which are apparently canon) showed us some more E-100s, this idea was abandoned.
With Amy appearing in Origins and Superstars and able to keep up with everyone else, her being a slow in Adventure is jarring. Something must have happened to her between Superstars and Adventure (or maybe as early as Sonic R since she was in a car) that made her much slower and unable to curl into a ball like a hedgehog would. And she wasn't fully healed until Advance 2 where she's back to her old self. It would explain why she's afraid of Zero when she could easily take it down Eggman himself before and since.
