You've explored most of Wishing Alps, so it's time to venture into Glamour Gulch to continue the main Wishblossom Ranch storyline in Disney Dreamlight Valley. The quest that grants you access to this area is The Decay of Fashion.
This quest is where you finally meet Cruella, and she's got quite a list of tasks for you to accomplish. It's a decently tough mission to tackle, so here's a complete walkthrough for The Decay of Fashion quest in Disney Dreamlight Valley.
