After you make your way up the Heights of Loneliness and learning Mason's story, you reach Zere Rocks.

Zere Rocks

This place is a perfect replica of Zere. It's as if someone used a copy machine—a Xerox™, perhaps?—to create Zere Rocks. There isn't much to do here. Just go into the northeast house. There will be a cutscene.

Don't talk to the slime yet. Read the books on the bookshelf across from the fireplace to learn some new recipes.

Get ready for a boss battle (you can use Zoom or a Chimaera Wing to return here to Zere Rocks if you need to heal and stock up on supplies), then talk to the slime. Then go outside to start a boss battle.

Garth Goyle

Garth likes to cast Kabuff and Magic Barrier, which will make it take longer to defeat him. Otherwise, just attack until it dies. It drops a Terrible Tattoo after the battle, but don't equip it. It's cursed, which means that you won't be able to unequip it unless a priest performs Benediction on you. You can either pay money at a church to get a Benediction, or you can teach your Priest the Benediction skill by spending 28 points on the Faith skill.

You are better off saving the Terrible Tattoo to use it as an alchemy ingredient.

Afterward, go down the stairs next to the house and talk to the ghost to receive a Fygg, then go outside. If you want to heal up before you continue, use Zoom or a Chimaera Wing to return to Slurry Quay or another location to heal up. Or if you want to proceed without teleporting, then use the south exit of Zere Rocks, and make your way around into the cave. Use the Evac spell or an Evac-u-Bell to return to the Heights of Loneliness at the base of the mountain. Use the south exit of the Heights of Loneliness, then go south, then across the bridge, then west to reach Bloomingdale. If you are starting from Dourbridge, go southeast and cross the bridge into the Lonely Heights area, then go south and cross the bridge, then go west to reach Bloomingdale.