Teenage Mutant Ninja Turtles (PC, 1989)

Teenage Mutant Ninja Turtles is a PC port of the NES game. Unfortunately, it has a massive design flaw in Level 3 that makes it unbeatable without cheating.

Debug Modes & Hidden Credits
The game contains two debugging codes, one which grants invincibility and the other which allows you to walk or swim through walls. Q + R + P is the invincibility code, and A + S + G 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 artists' names are scrawled out in huge letters on the screen.