NUFLI
A C64 picture format that pushes the machine toward per-pixel color by stacking the FLI trick on top of a sprite layer that also hides the FLI bug.
NUFLI ("New Underlaid FLI") builds on FLI, the trick of reloading the video-matrix pointer on every raster line so color can be set per 8×1 block instead of per 8×8. On top of that NUFLI lays an underlying layer of sprites — partly for more color, partly to cover the notorious "FLI bug," the strip of garbage on the far left that appears because the VIC-II can't fetch fresh color data in time after the line shift.
The format is a still image, not a usable mode: nearly all raster time and CPU go into feeding the VIC-II line by line. Pictures are built in a converter on the PC and shown by a small viewer on the C64. The result lands well beyond ordinary hires and became a staple of the C64 scene's graphics competitions.