There was a span of a year or two when I could literally write 68000 machine code by hand, without needing an assembler, due to an obsession with sprite blitter

There was a span of a year or two when I could literally write 68000 machine code by hand, without needing an assembler, due to an obsession with sprite blitters culminating in a bit of code which would generate arbitrary custom blitmask functions as part of the image-loading process. I had very little understanding of "abstraction" at the time, so it pretty much just built instructions from the bits up via shift and mask operations. I would never do anything like that now[1] - but I'll always be proud of the day I dropped into Macsbug, picked out a section of memory, wrote myself a minimal Tetris implementation, moved the PC (aka IP register) into it, and played. It crashed, of course, but the fact that it even sort of worked felt pretty good. 1 - possibly not strictly true in the literal sense as I still have a soft spot for these sorts of hacks