Probably not hardest, but one that sticks in my mind was that I downloaded an old copy of Jedi Knight II onto my computer and was excited to play it again... bu

Probably not hardest, but one that sticks in my mind was that I downloaded an old copy of Jedi Knight II onto my computer and was excited to play it again... but it crashed on launch. Or rather it would throw a modal dialog (complaining about graphics something-or-other) and go into a loop of system beeps. So I attached to it with gdb... and started going down a rabbit hole of stack traces and assembly code. I don't remember ultimately what the problem was (I think the code had been (partially?) stripped of symbols) but I do remember ultimately flipping a bit in some conditional that finally got it to launch!