From the SS thread discussing spider multi-ball, it occurred to me that there might be other not so well known modes on other titles that continue to elude you....For me,
ST:TNG warp 9.9. Even if you cheat and start at warp 4, it still takes 15 loops to get to 9.9. I got to 9.7 a few times but never closed the deal.
Another one, that I did complete, but it's not easy is move your car on CFTBL. Getting all the way to the nuke.