Sonic CD (2011)

Sonic CD is a modern-day recode of just your average Sonic the Hedgehog game on a CD...

Swipe & Tap


Left next to another unused menu selection (below), this appears to have been a cut feature from the Android and iOS versions, most likely putting touch controls to use.

D-Pad


Unused because, technically, D-Pad's your only option.

Final Fever


While "Final Fever" is the title of the Japanese final boss theme, Taxman (the lead developer) stated that during development this Final Fever was to be the name of a new boss stage, although it was cut due to Sega wishing to remain faithful to the original game.

As this text was found among what seems to be an early Stage Select, it is safe to assume it used to represent this cut boss.

"Sega CD BIOS" Sonic


A sprite of Sonic most notably used during the Sega CD BIOS boot. As it is present next to Sonic's sprite for the character select screen, it is safe to assume this once occupied that slot before the newer sprite took his place.

Upside-Down Tails


Interestingly, while all of Sonic's unused sprites were removed from this port, Tails got his own unused animation based on one of Sonic's!

SCRIPT


No idea, honestly. Probably something related to the Retro SDK's level editor from which the game was built.

Time Attack
Just your usual "?" placeholder. Not much else to see here...

The image that occupied the Exit selection of the Time Attack screen in the Sega CD and 1996 PC versions.

Desert Dazzle
According to Taxman, Desert Dazzle was a new level he was working on that ended up being cut for time and authenticity reasons. This image can be accessed by entering the Sound Test code 8, 32.

Accessing this image will also take you to the Stage Select with Tails as your character.

Retro Engine Dev Menu
hRGDDDODIzs Set byte in GameConfig.bin to  to access this menu from the pause screen.

Regional Differences
In all Western releases, the non-highlighted palette of the menu text is a grayish hue. The Japanese version has a white hue for this text, as well as the expected translated text. In addition, it was not released for consoles in Japan, nor can it be found on the Japanese Steam store.