The thing about the VIC II and SID is that they have just enough flexibility by exploiting the HW to pull off an astonishing number of effects, like stretching

The thing about the VIC II and SID is that they have just enough flexibility by exploiting the HW to pull off an astonishing number of effects, like stretching sprites/screen/characters by tricking the VIC to redisplay lines, this allows cool HW scaling effects. Or getting the VIC to delay displaying lines, which allows shifting the screen by more than 8 pixels in vertical and horizontal directions (the scroll registers normally only allow 8 different pixel positions) People have exploited interlacing/sub pixel/NTSC/PAL effects to generate new colors, or simulate hi-res. They've combined changing color palettes per-line with sprite overlays to breach the barrier of 4 unique colors per 4x8 pixel block. The list of surprising effects I've seen on the C64 never seems to end. Some crazy people have also managed to get the C128's VDC to do demo-scene effects as well. One trick I was working on in the 80s before I quit the C64/C128 to go to the Amiga was to try and use the C128's MMU chip to run high speed 8502 code. The C128 MMU could remap the 0 page addresses ($00-$FF) into other memory regions. Because 0-page instructions run faster (e.g. STA $C000 vs STA $C0), if you could remap zero page, you could write code in a style that is significantly faster. I wanted to use this to write a fast line drawing/poly-filing routine. Since the VIC could also be remapped by the MMU, in theory (I never go to to test it), you could map the zero page to a VIC mapped address, and do pixel block operations at 2-3 cycles per write.