The Immortal (NES)
CPU Register Debug Screen
It is possible to get this screen to appear by entering a valid password that gives invalid stats, such as 993syyyyyyyyy which should give you 15 hitpoints, 255 power, everything in the inventory, 2550 gold and on level 15. The middle character, "X", no longer exists in the game's font and appears corrupt as a result.
Although the game waits for the player to press B to continue, the code seems to be broken, and the CPU will eventually hit invalid code and lock up after the button is pressed a certain number of times.