Sonic CD is a 2D platformer built around time travel. You race through zones that exist in three states—past, present, and future—jumping between them by hitting speed posts and maintaining momentum. The goal isn't just reaching the exit: you hunt down robot generators in each zone's past to prevent a bad future, or collect Time Stones from special stages to unlock good endings. Levels shift aesthetically depending on whether you've altered history. Dr. Eggman's planted machines across Little Planet, a world that appears once a year above Never Lake. If you destroy his tech before it spreads, future versions of stages become lush; ignore them and they turn industrial. It's Sonic with a puzzle layer—speed matters, but so does which era you're in when the goal ring appears.
