There is a secret statue room in Sonic Generations. It can be accessed by holding back (Xbox 360) or select (PS3) from the Collection room. Statues are obtained by entering codes originally found in specially marked Sonic Generations merchandise and now freely available online.

Due to its returning cameo in the background of Radical Highway on the 3DS version, NiGHTS is the only non-Sonic character to appear in Sonic Generations.

Similar to the missing posters of Ray and Mighty in the City Escape level, wanted posters can be seen of Fang, Bean, and Bark; three characters from the Sonic The Fighters game. The 'Wanted' status could both a reference to them being criminals, and due to the fact that fans often request for these three characters to be put into a new game.

After finishing Green Hill Zone as modern Sonic, Sonic will mention to Tails that the area seems awfully familiar, with Tails saying "not to me." Green Hill Zone was from Sonic 1, while Tails didn't come into the series until Sonic 2, meaning Tails would have no memory of the area.

Perfect Chaos' appearance in this game is different to its appearance in Sonic Adventure; in Sonic Adventure, it was a creature made entirely out of water, whereas in Sonic Generations, it has scaly, reptile-like skin. According to an interview with Takashi Iizuka in the Prima Strategy Guide for Sonic Generations, Perfect Chaos' 2011 design is how the team had originally planned the monster; it had had to be changed in Sonic Adventure due to the technical restraints of the Dreamcast.

Mighty The Armadillo and Ray The Flying Squirrel can be seen on missing posters in city escape. They've been missing since 1993, the year SegaSonic the Hedgehog was released for arcades, where they were first introduced.

Jaleel White, known for his acting as Steve Urkel in the 90's sitcom "Family Matters", was considered by SEGA to be the voice of Classic Sonic. Jaleel was considered because he had previously voiced Sonic in "Adventures of Sonic the Hedgehog", "Sonic the Hedgehog" (1993), and "Sonic Underground". Sega ultimately decided against casting Jaleel, resulting in a mute Sonic.