Sonic Generations/Continuity Nod

"(In Colors) Cubot: "Your plans have been crushed by Sonic for, like ever. He stops you like it's his job or something."
 * Tails remembering that he's never been in Green Hill since he wasn't in the series yet.
 * This game's version of Green Hill Zone has an expansive, flooded underground area, similar to the Master System/Game Gear version of the first Sonic game.
 * At one point Sonic repeats a line almost directly from Sonic Colors:

(In Generations) Sonic: "Seriously, we beat this guy every time. It's like it's our job or something.""


 * Some characters appear in stages that they were in previously. To list:
 * Knuckles in Sky Sanctuary
 * Amy's case is unexpected: While she is featured in Chemical Plant, the boss race against Metal Sonic in Stardust Speedway follows after that level, and Amy originally needed to be rescued from there.
 * Rouge in City Escape
 * Cream & Cheese's appearance in Speed Highway is unusual as well: Cream makes a cameo appearance in Sonic Adventure DX, which was released near the time of Sonic Advance 2, her first appearance in the franchise.
 * Espio in Seaside Hill
 * Blaze in Crisis City
 * Charmy in Planet Wisp
 * In Sonic Unleashed, Dr. Eggman mentioned that the Egg Dragoon you fight with the Werehog was a prototype. You fight the final version in Generations with Modern Sonic.
 * It bloody shows.
 * At the end of the game, it is revealed that
 * In the English pre-final boss cutscene,
 * At the end of Sonic Adventure, Sonic says to Perfect Chaos "Hey, I'll play with you some other time."
 * When Rouge and Shadow appear to cheer Sonic on before fighting the Time Eater,
 * Modern Sonic first gets a tutorial on Light Dashing in Speed Highway -- Sonic Adventure was the first game to give Sonic that ability. On the same note, the first tutorial on walljumping is in Seaside Hill, which gave the 'speed' member of each team a walljumping ability -- including Sonic.
 * The final boss
 * After the credits,
 * This is followed up by considering going for a teaching degree, a possible nod to Sonic's Schoolhouse,.
 * A subtle one occurs within the levels. The springboard from Sonic the Hedgehog 2 appears in this game, in Classic Sonic's stages. What should be noticed is that Green Hill (the level from Sonic 1) is the only level that doesn't seem to have them, while it was introduced in Chemical Plant (the level from Sonic the Hedgehog 2).
 * There's also a small one in the cutscene where Sonic finds Knuckles-- who immediately preforms a watered-down version of the Spiral Upper upon being unfrozen.