Sonic & Knuckles

Another easy one to get - all you need to do is accumulate 100 rings at one time... there are plenty of rings in every level so you shouldn't run dry of rings providing that you take your time to avoid any hazards which may cause you to sacrifice every ring you have at the time of being hit.

If you want to try to head into the bonus stages (not the 3D special stages) to score even more rings without the risk of losing any (albeit the slot machine which, if your unlucky enough to get 3 Robotnik icons in a row, you will lose 100 rings).

If you are struggling for whatever reason - use the save anywhere feature on the pause menu.

The best way to focus on this achievement without risk off being injured is to enter the special ring stage. The slot machine will often pay out 10 or 30 rings. To prevent losing 100 coins save at the beginning and after every big score. That way, if Robotnik comes up, you will not lose time.