Pestilence's ring is a ring that helps the Green Horseman, Pestilence, channel and focus his powers. Sam and Dean obtained the ring after Castiel cut off Pestilence's fingers using Ruby's knife.
When combined with the other three horsemen's rings, it can open up a portal to send Lucifer back to his cage again.
Trivia
- The wearer of this ring gains the title of Pestilence and all of his powers.