R2

R2 is a reference to a deleted level from Sonic CD.

Proving its existence is possible by examining the game files on a PC. When examining the level files the levels skip from R1 (level 1, Palmtree Panic) to R3 (level 3, Collision Chaos) There is no R2 to be found. It's existence is also proven by using the level select menu. When switching between levels it skips from level 1 to level 3, again leaving out level 2. Finally, if a player gets a low enough total time in the time attack mode, a pencil test movie is unlocked. One scene shows Sonic running around and dodging a worm-like badnik in what looks somewhat like a ruinous setting. In an interview, Jim Tretheway, a developer for the game, stated that the level was likely cut because it didn't meet quality standards.

In the 2011 remake of the game, a single image of an unfinished, desert-themed zone called "Desert Dazzle" was found. While not directly confirmed, this could have taken the place of "R2".