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) to R3 (level 3), 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. In an interview with Jim Tretheway it was stated that the level was likely cut as it didn't meet quality standards.