So yeah, checkpoints. Finally, long levels will not be tortuous!
Also, speaking of torture, 100 Mario Challenge Expert Mode. I think Nintendo knew this would be plagued by terrible levels, and that was actually the point, hence why only an expert could possibly hope to beat it. Just a theory, but if so that's just sadistic Nintendo :P
I'd post my levels but with the exception of one (which is just a "HARDMODE" version of the one right before it) kinda suck. And i don't have the codes handy atm. I'll get the code for that one and it's original easier version that still only has a 9% win rate somehow (seriously... you can fly over the whole thing with a running start XD)