Sonic CD is a side-scrolling platform action game where Sonic the Hedgehog and his self-proclaimed girlfriend Amy Rose travel to Never Lake. They discover the legendary Little Planet, tied in chains and covered by metal, which has been manipulated by Dr. Eggman using its powers. He created Sonic's evil counterpart, Metal Sonic, who kidnaps Amy and disappears.
Sonic CD features fast-paced gameplay similar to other installments of the series. Sonic uses his spin attacks to destroy enemies and collect items like protective rings, shields, and speed shoes. His special attacks include the Spin Dash and the Super Peel Out. A unique feature is Sonic's ability to travel to past and future versions of stages he traverses.
Time Stones can be collected by completing special stages where Sonic has to shoot UFOs within an allotted time limit. The game's "good" ending can be achieved by collecting all seven Time Stones or turning all future level versions into "good". With over fifty levels in total, the game takes advantage of the Sega CD format with features like CD audio, video clips, and more.