I haven't found any debuggers in games but I have exploited bugs. An old game called Shogun had a part of the map where you could slip by some barriers and go to screens off the map that weren't meant to be seen (just blank screens). I used the blank areas to take all the items in the game and store them to prevent the npcs from annoyingly picking them up. It was also a quick way to jump to areas of the map without going through all the normal screens to get to the same areas.
One time I copied Thexder to another 5 1/4 and used a hex editor on the main .exe. I randomly typed a bunch of characters into the hex editor and saved it. Amazingly it still ran and I was shocked that I had unlimited energy to shoot all I want and unlimited shields so I could never die. It ran perfectly and never had any errors. I think the odds of achieving that randomly are a googleplex to one.