Debug Modes & Hidden Credits[]
Hidden Credits accessible via debug codes.
The DOS version of the original Teenage Mutant Ninja Turtles video game contains two debugging codes, one which grants invincibility and the other which allows you to walk or swim through walls. Q + W + E + R + T + Y + U + P is the invincibility code, and A + S + D + F + G + H is the no-clipping code.
The no-clipping code in particular will also allow you access a hidden area in Level 2 (the underwater portion of the dam area) where two of the programmers' names are scrawled out in huge letters on the screen.
Source: Flying Omelette