Classic Sonic, Modern Sonic, Classic Tails, Modern Tails, Knuckles, Shadow, Silver, and Blaze have been modified, making them resemble their Super Forms (or Burning Form, in Blaze's case.)
Classic Metal Sonic uses a new "Classic" version of Neo Metal Sonic's design.
A pre-made save file with 10 overpowered skill sets. These 10 skill sets use more than 100 skill points. Additionally, Modern "Super" Sonic's skill sets utilize a few Classic-only skills, and Classic "Super" Sonic's skill sets utilize Modern Sonic's Acceleration (and serial homing) skill(s). This save file will not affect your original save file. When you disable Super Sonic Generations, the game will use your original save file.
The Acceleration skill gives a much greater Speed increase than it does in the un-modded game.
The Barrier, Ring Time, Power Sneakers, and the 3 elemental shields can all be used 5 times within a single stage, instead of only once or twice.
Modern "Super" Sonic can now utilize the Barrier, Ring Time, Power Sneakers, Invincible Start, and the 3 Elemental Shield skills. Do note that Modern "Super" Sonic is unable to utilize the extra "jumps" granted by the Elemental Shields.
The "Super Sonic" skill has been changed into a "Hyper Sonic" skill. Upon collecting 50 rings, either "Super" Sonic can transform into Hyper Sonic (from Sonic 3 & Knuckles.) When using the correct settings, Hyper Sonic is a LOT faster than normal, and only loses 1 ring every second (instead of losing 2 or 4 rings per second.) However, the increased speed makes Hyper Sonic hard to control. Additionally, Modern Hyper Sonic now lacks the auto-pilot boost-flying that the "Super Sonic" skill had.
Super Sonic Generations comes with 3 "mods". "Super Sonic Generations: Main Files" features Super Sonic, Hyper Sonic, and a few of the HUD elements. "Super Sonic Generations: NPC+HUD Files" has all of the other characters, and the rest of the HUD elements. "Super Sonic Generations: No Auto Pilot Flying" disables the ability to fly over the stages while boosting.