I'd love to rom hack invulnerability into Sonic CD for the Sega CD. The thought of blazing through this gem without taking damage of any kind has a real appeal. I did hack the rings which is almost good enough but you still get knocked back when hitting an enemy or spike so it's still task that needs to be done.
999 rings when hit: 73 instances, change all
Replace with: 33FC00FF00FF1512
1 ring = 7: 73 instances, change all
Replace with: 5E7900FF1512