All Red Star Rings Found! Achievement
All Red Star Rings Found!40
Defeat the final foe after collecting every Red Star Ring.
In every non-boss Act there is one Red Star Ring to get. After you have them all beat the final boss.
Note: Any Red Star Rings you get in Co-Op are carried over to your Single Player game. If you get a Red Star Ring, pass a checkpoint, and then die you will keep your Red Star Ring. If you get a Red Star Ring and die without passing a checkpoint you will have to obtain the Red Star Ring again.
Here are some videos to help