I wrote a "chaos monkey" script in MAME's Lua scripting engine that semi-randomly presses keystrokes to exercise every path in Copy II Reboot, and it helped me eventually nail down a combination of actions that can put a Superdrive in a permanently-busy broken state where the drive ROM freaks out and fast-fails every time you call it and manipulates the stack in a way that crashes the caller. So that's fun. (The bug also exists in Copy II Plus v8.4.)