With the use of the "Characters In any levels code," we can access a hidden test level normally not accessible. This level has no music, no ending, and no way to die. It tests grinding, walking up slopes, walking across bridges, as well as numerous other things. To access it, enter the following Action Replay code, and select any stage at the Stage Select. Once you select the stage, hold up on the D-Pad:

BPMU-HT2R-X7BA2
Q95B-WV0J-10V85
H2E9-MAE2-U5PEE

Tails can play this level without his mech, however a sort of 4-Player splitscreen comes with him.