Slime & Ring is an early sidequest in Secrets of Grindea, but the vague instructions make it confusing to complete. Here's where to find Bella's ring for the Slime & Ring quest in Secrets of Grindea.
The Ancient Temple Enter the Pumpkin Forest Find the Ancient Temple Secrets of Grindea (Quest)
To start Slime & Ring, talk to Bella in Evergrind City. You'll find her in the northwest part of the city, to the left of the entrance to the Collectors' HQ. She'll tell you that she lost her ring somewhere in the Pillar Mountains and asks you to find it for her. However, Bella doesn't mention any specific area in the Pillar Mountains, and the quest tab in your menu doesn't give you any hints.
Related: How to Defeat the Giga Slime in Secrets of Grindea
Pillar Mountains is located northeast of Evergrind City; you drove through it on your way out of Startington. It's a large area, and the ring doesn't spawn in a set location. To get Bella's ring, you'll need to search all of Pillar Mountains for a green slime with the ring inside (pictured above). This slime is easy to miss, as aside from the vague outline of the ring, it's visually identical to the other slimes in Pillar Mountains. Find the slime and defeat it to get Bella's ring.