This is a bit of a quickie as I'm posting this from the comfort of my bed, but it is too awesome not to share.
Download it and play it. NOW.
Essentially, the rings have been turned into onion rings and each one makes Sonic fatter, making his speed go down and can barely jump until he is too obese to move. There's been mods in the past where the rings cause death, but this is special.
It adds a whole new challenge, as you can lose weight by running back and forth and also with some item boxes. Plus, you still need one ring to survive (and to rule them all, maybe?).
I can't get past CPZ without cheating, but the amount of love that has gone into this with new sprites is incredible.
GO PLAY IT